Weight, weight, weight. I think a 17 would be fine if you got a forge wheel that
fit the car. I do not know which would be better, given the same size tire. It depends on how the suspension behaves. My point is really that the thinest side wall is not the best and getting ride of unsprung weight instead of adding it is the way to go. Honestly, I would look at what similar cars run. I just suggested the 16" because they are cheap and light and with a properly sized track tire would work well.