K-69:
Howse about some pix of the new set up? Will be interested in hearing your track day results. Wider means more frontal area and these things are already bricks. So maybe what you gain in the curves you lose on the straights? Also wonder if they are too big, and your car too light, for them to warm up to optimal operating temperatures.
GRM recently looked at wheel weight and , surprisingly, didn't find heavy wheels made the car slower, despite all the theory to the contrary (Un-sprung weight, rotating weight, etc.).