Anyway in this tourney style type game with more Pershings and Jadgpanthers on the table than were ever in the war how well does the type of American force do on average in games.
Unfortunately that is one of the major misconceptions a lot of people have about Flames of War.
I do not have the Bridge at Ramagen book yet but that is what is suggested in order to run the Grimbal's Beasts set.
And that is one of the major reasons why. People assume things without checking them out. You really need to go get the book. It's necessary for the game and it's a great read. And yes, the Flames of War people know about history and really do go out of their way to use it.
With that said, and unless you're playing some goofy pick-up game where "anything goes", you're going to be fielding an "army" based off of one of the lists in the books. They ARE based on reality.
So the bad news for you is that you'll never field a hoard of Pershings. You might field a small force of them. You'll only ever get a single platoon and you can field 1-5 vanillas or a single super which is how they were fielded historically. So no, you won't be able to field more in a game than ever really appeared on the battlefield. Now there might be a zillion Pershings at the tourney because everyone wanted to field that list, but no, reality holds sway here. And sadly for you a savvy German player will still outgun you, to a degree, and might actually outnumber you!
Pointwise you're already at max points! That is assuming you have the Grimbal's Beasts, and a 5 tank platoon box, and you're going for the Confident Veteran 9th Armored Division. So basically you'll have a late War US armored company with a platoon of Panther equivalents. The bulk of your tanks are still Shermans. With your boxed sets you'll have 8 Shermans (2 command and 6 to split into two platoons (620 points), 3 Pershings (595 points!), and an armored rifle platoon (295 points). So you're 1510 with just the tanks and infantry and you haven't even tweaked your Shermans yet!
Now I'll grant you, the Pershing is a solid tank. You get 10 armor up front and a 32" 2 ROF 14 AT 3+ FP gun. And the super Pershing gets an even better gun and more armor! BUT, they are expensive! So You only get a SINGLE platoon and you have to choose between either vanilla platoon with 1-5 tanks or a single super Pershing who costs 275 point all by his lonesome! You can take the Reluctant Veteran 3rd Armored Division to save on costs but you know how hard it is to get Reluctant Veterans moving when bullets get tossed around and as a tank company you're nearly always going to be attacking! Fortunately the Pershings are always Confident Veterans.
I think I personally would go with an Armored Rifle Company and stick with upgraded Shermans. You'll have a larger force that is more balanced point wise and has big, solid platoons. Then I might consider arty and air units.
But seriously, get the book and read up on what you're getting into and to get a feel for what you're facing.