AFAIK, the issue with Project Cars is that it's using PhysX for car physics simulation (there's no other alternative than to use PhysX).
If you're using a nVidia card, it'll do PhysX through the graphics card. If you own an AMD/Intel card, it'll have to use the PhysX CPU path.
And the biggest problem here is the PhysX CPU path, which is purposely botched. IIRC, it's locked onto a single-thread and uses ~30 year-old x87 instructions for floating point operations instead of the much faster SSEx (yeah nVidia did a really good job at
crapping over other IHVs again optimizing for their own hardware).
Had the game used another physics engine (e.g. Havok), none of this would've happened.
Which is probably why we have never seen PhysX being used for anything other than visual effects that you can switch on/off or some periodic and light physics simulations.
It's too bad that Slightly Mad Studios couldn't see this before the shit hit the fan.
Like I said,
Gameworks deals are like peeing in your pants.
I've seen reports of a DX12 build of Project Cars running about twice as fast for AMD GPU users. Basically, freeing up CPU resources with the new API leaves more time for the CPU to run all those super-inefficient physics simulations.
To summarize:
- Terrible performance on Project Cars in AMD/Intel GPUs has little to do with AMD drivers. Don't use PhysX in simulations that you can't disable. Avoid Gameworks like the plague.