One thing to bear in mind is that by 1970, Georgie had been dead for over two decades. The main technical adviser for the film was Omar Bradley (by then the only surviving 5-star General) who really never liked Patton. The film itself was based on Ladislas Farago's book "Patton: Ordeal and Triumph" and Bradley's memoir, "A Soldier's Story." Historian Carlo d'Este has written a much better treatment of Patton in his "Patton: A Genius for War" published in 1995. Bradley, for his part, collaborated with Historian Clay Blair to write "A General's Life" published shortly after the old man's death in 1983. There has been no independent magisterial biography of Bradley that I am aware of. He deserves one.
"My own feelings on George were mixed. He had not been my choice for (3rd) Army Commander and I was still wary of the grace with which he would accept our reversal in roles. For George was six years my senior and and had been my Army commander when I fought II Corps in the Sicilian campaign. I was apprehensive in having George join my command, for I feared too much of my time would probably be spent curbing his impetuous habits." - Omar Bradly "A Soldier's Story"
For his part, Patton could be equally scathing in his attitude toward Bradley:
"On the other hand Bradley has many of the attributes which are considered desirable in a general. He wears glasses, has a strong jaw, talks profoundly and says little, and is a shooting companion of the Chief of Staff (George Marshall). Also a loyal man. I consider him among our better generals." - GSP Diary entry 18 January 1944
It is a credit to both men that they subsumed their personal feelings to the job at hand (that happened a lot in WWII) and worked to use their innate strengths to cover the other's weaknesses - both real and perceived.
As to the "Ike" portrayal: Patton was a bit-part player in the OVERLORD drama. He had been secretly appointed to command US 3rd Army but had no troops or equipment to speak of, in fact he couldn't even speak of that. He was publicly named to command the "First US Army Group" headquartered in Kent across the Dover Straits from Calais which is the historic route for invasions in both directions. FUSAG as it was known was even less of a command than 3rd Army in that it was entirely made up of dummy formations with dummy radio traffic and complete with inflatable tanks and trucks that were assembled and disassembled at various places to simulate troop movements. Patton was in no way a part of this other than to be seen at events in the area with full panoply of staff and ceremony. It was as a part of this latter that he gave the infamous Knutsford speech where he made a joke about the US and Britain "ruling the world."
It's hard for us to realize, some seventy years hence, just what kind of firestorm this set off. The State Department was, at the time, basically a branch office of the NKVD (McCarthy was absolutely right about this) which was ever alert for signs of a weakening of US/British support for the Red Army. Patton, being a hard-core and outspoken anti-Communist was, of course, Undesirable #1 in the US Army, so anything he said was going to be leaked and amplified. Also, don't forget that the VPOTUS at the time was an avowed Socialist, Henry Wallace. The leftist oinking made its way to the White House and Congress who then complained to both Ike and Marshall along with demands that *something* be done about it.
"Apparently I am again in an incident due to a three minute talk I made at a gathering of some 50 people at which, by the way. the chairman (she was a woman) said I was unofficial. I feel pretty bad today as anything may happen, but at least I still have the When and If (his boat). I may be using it soon.
"It is a horrid thought that one may be deprived of doing the only job one is good at due to the exercise of free speech, but that thought is always with me - it is a wonderful morale builder!?!?!
"Bah! Jesus only suffered one night but I have had months and months of it, and the cross is not yet in sight, though probably just around the corner." - GSP, letter to Nina Patton Totten 27 April 1944
Patton figured this was the end of his career. He undoubtedly knew or at least guessed the gist of a message that Eisenhower had sent to Marshall:
"I have grown so weary of the trouble he constantly causes you and the War Department, to say nothing of myself, that I am seriously contemplating the most drastic action." DDE cable to GCM, 30 April 1944
The version of the Ike/Patton meeting of 1 May 1944 as shown in the "Ike" film is right out of Eisenhower's own book, "At Ease: Stories I tell to friends."
"(I)n a gesture of almost little boy contriteness, he put his head on my shoulder ... this caused his helmet to fall off - a gleaming helmet I sometimes thought he wore in bed. As it rolled across the room I had the rather odd feeling that I was in the middle of a ridiculous situation." - quoted in "Eisenhower: A Soldier's Life" by Carlo d'Este
Ike let Patton stew for another day then sent him a telegram:
"I am once more taking the responsibility of retaining you in command in spite of damaging repercussions resulting from a personal indiscretion. I do this solely because of my faith in you as a battle leader
and from no other motives." - DDE to GSP, Jr., 3 May 1944 (emphasis added)
d'Este speculates that one reason Patton was retained was that the only other man either Ike or Bradley could countenance to lead 3rd Army was Lt. General Lucian Truscott who had just assumed command of VI Corps on the Anzio beach-head in Italy and was thoroughly occupied cleaning up that epic mess and near disaster.
As an aside, the monologue Scott/Patton delivers in the scene after this meeting is straight from Patton's diary entry for 1 May 1944. This includes the famous, "His will be done."
As to Scott's portrayal of Patton I will relate a story. One of Patton's former friends who had also served on his staff and was now (1970) in his dotage went to see the movie with others. He reportedly was amazed but still upset. "Dammit! They got Georgie to do this movie but why the hell couldn't they get Coddie?" He was referring to Col. Charles Codman, Patton's Chief of Staff. Scott's portrayal was so spot-on the old man thought it WAS Patton in the film!
The whole Montgomery/Patton dispute was quite overstated in the movie particularly in the post D-Day scenes. By that point Monty was an Army Group commander which was a whole command level over Patton's as commander of a numbered field army. It's like the difference between being a D-1 head coach and a head coach in the NFL. When 3rd Army became operational on 1 August 1944, Bradley assumed command of XII Army Group and was then Monty's equal in the command structure. By the end of the war, Bradley's command represented the greatest combat formation of American troops under one commander in history. XII US Army Group consisted of 1st US Army (General Courtney Hodges), 3rd US Army (Patton) and 9th US Army (General William Simpson) and 15th US Army (Gen, Leonard T. Gerow) for a total force of about 1.5 million men.
In the end, BOTH films would seem accurate in their portrayal of Patton at particular times during WWII. It is that very complexity of his character that makes him one of the most fascinating and successful commanders in American military history, a distinction he shares with "Stonewall" Jackson and Douglas MacArthur.

Bradley, Eisenhower and Patton (US Army)