The lies of Slightly Mad (Project Cars) Head of the studio confess that they were overpromising

[torok]

Barkley said:

Yeah it's not good, they should just scale it back more if that's what needs to be done. 540p that bugger if you have to.

It isn't necessarily limited by the GPU. It can be CPU bound, since racing sims have some load of physics on the CPU. Wii U's bottleneck is the CPU (that's basically a tri-core, overclocked GameCube CPU), not the GPU.