15x7 here. 15x7.5 is probably better for ultimate grip. You could run the Toyos in 195-50-15. Currently the hot setup for STS in Autocross. Let's see how I do this season with my 205-50-15 Advans in STF.
15s give you a great choice of tire sizes as that is what all the Fast ST Honda Civic Si and CRX run and NA/NB Miatae in STS. Also Miata in e-stock have a nice selection available as to SM cars which also use 15x7 wheels.