I tested the frame rate before and after Y21 in South City in the BMW F1 car and before hand i had to take off alot of graphics or low to get it running at 30fps. After i downloaded Y21 i felt no improvement, FPS stayed at 30fps. I put all the graphic settings full or best, and it stayed at 30fps.
So, i dont know how it works, but its ok, but VERY confusing!