Running triple screens at native 1440 resolution currently is not really realistic with ACC.
I am running 1080 triples @ only 60Hz with a single mildly overclocked 1080Ti and otherwise fairly recent beefy computer and am getting good, smooth constant 60 FPS at all weather conditions with a proper grid (unlocked at ~70-90 FPS) with a mix of Epic and High settings and a few key settings like volumetric particles to lowest settings.
One reason why triple screen setups suffer so badly in ACC currently is the necessity to run the image warping workaround of the UE4 engine to bend the distorted side monitor view a little more into shape and THEN to slightly improve the atrocious resulting image quality run a ~120 (or more if you dare) resolution upscaling and higher sharpening values than ideal (I use a value of 0.7 or 0.8 with 30deg angled side monitors and it is acceptable in geometry, image quality though is horrendous compared to any other racing sim at native resolution and proper multi view rendering).
The image quality is very, very bad currently but to be honest the magnificent physics do make up for it.
I could not possibly imagine any computer that would run ACC currently at native 1440 resolution with triple screens, decent graphics settings and the needed image warping workaround if a single 1080Ti can barely make do at 1080@60Hz.
I have no idea if SLI setups currently work with ACC in this early build and if how big the actual benefit is).
In my setup the 1080Ti is the limiting factor for ACC (under constant full load while the CPU cores lounge in a mild breeze, sipping cocktails at barely 60% load and neither RAM or GPU memory is working hard.
You cannot buy a GPU that is available today to do what you ask :-( I suggest to run ACC at 1080 (you should get a decent performance at mid graphics settings), wait for ACC to be properly optimized (another 6-10 months after the 2019 content perhaps) and upgrade your GPU then.