Yo, OP. I built a racing rig last year and struggled for a while with this very question. I also went 3x 1440p, at 144hz. A lot depended on pricing at the time because I was taking my time with limited deals and just waiting for the right prices.
the good thing about pretty much all of these games is that they aren't very demanding so while certainly very high, the pixel count you are trying to push isn't really as much of a struggle as it sounds. Assetto Corsa, modded up with custom textures and all that, however, can be a problem.
Anyway, I went with a 6800XT which at the time was quite hard to find but I eventually got one at the local MicroCenter for just under $600 ~last December, I think. I'm able to get about 90 FPS @ "high" settings and that's more than adequate for me. I think I have managed 110 in some games. I paired the 6800XT with a 5700X (another MC deal + mobo). Today, you'd probably want to look at the 7900XT and above cards. The 7800XT should be fine, I suppose. For Nvidia, whatever the similar class is, but make sure they aren't robbing you of VRAM. Don't even consider anything with less than 16GB.
I don't think I've tried running FSR because I don't really see a point to it--also I haven't played the F1 games, mostly due to poor reviews and that everyone says that you're better off with Assetto Corsa and mods, anyway. I mostly play Assetto Corsa Competizione, though, even though I primarily wanted to do F1 racing.
I have the Next Level rig that can adjust from GT to F1 position, which is quite nice, but I also find that once you find a preferred style, you probably won't be switching back and forth very often. this rig is also one of the shortest bases and has real limits to where you can attach the DD mounts, so if you are super tall, I wouldn't recommend that one if you haven't already purchased something.
What other hardware are you looking at? If you are in the US, I found that ordering direct from various European companies was a lot cheaper than finding them here, either online or at a store (Micro Center also sells a lot of this stuff). Digital Motorsports and, I forget a couple of others, have free shipping on everything to the US, and not paying their VAT, everything ends up about 15% cheaper doing it that way.
Oh, you mentioned Forza....be aware that it uh, doesn't work very well, if at all, with a proper DD motor. I went with a Simucube 2 and the only way to get Forza to recognize anything that isn't a crappy belt-driven Logitech, is to use a separate emulator software to map your steering controls and hope that it works through Forza. I struggled with this and it just never worked for me. My main wheel uses an Ascher Racing button pad, which is quite nice, but doesn't play well at all with that software or Forza, despite some clear instructions on how to get it to work with Simucube. If you have a Fanatec, it's probably a bit more friendly. Also to note, Fanatec is overall probably a bit easier to deal with, certainly a lot cheaper. Simucube does limit you in a way to the most expensive wheel setups, so definitely do take that bit of advice seriously. Also, Forza would be the most demanding title for this setup and, as I never got it to work, can't really offer advice on GPU there. It sucks though, as I'd really like a good arcade game to run on this thing. All of the serious simulator games are very hard, and very stressful.