This won't be something AMD or devs can fix. Its because of heavy usage of PhysX in their game engine from day 1, they knew performance would be horrible for AMD.
The console version is toned down to a point where console players complain the game feels like an arcade and not a racing sim. Its physics is already messed up. On the PC, PhysX is run to the max, their software engineer knew about it, he was the one who fessed up on their forums. His suggestion for AMD users is to tone down all the settings for now. No other way around it.
Under no normal situation would a gtx660 smack down on a R290X except for PhysX being GPU accelerated vs CPU only. This is the exact thing we've seen for years with running PhysX on AMD, and in Project Cars, the smoke is GPU PhysX accelerated. Do a burn out on an AMD rig, slideshow.
@DarkKnightDude Try it and see.