There is a discernible difference between a 6" and 7" rim on a 205 series tire. Any good driver (it's pretty common knowledge amongst the R-DOT SCCA crowd) who has done testing will tell you this. However, a 7" rim would help to make the TR4 more competitive against the Porshe 356's , the Kumho / Toyo shod MGBs and those pesky 1000lb Super 7's and Ginetta's <hint: Jack W>