Ok, lets sum this up. I personally think 20's look good on the new stang, especially with the wheel gap gone. However, how much performance/braking are you trading by going with such a large wheel?
On a side note, what is the widest tire you can get on a 20x 10 rim?
IMO 20's and up are too big. 19s arent bad but I am going to go with 18x9 in the front and 18x10 out back in deep dish bullits. I think anything bigger than 18 is a waste and too much unsprung weight.