you could always try and get yourself a set of 300zx rims. they are about a 7.5" rim, so you could run 225/50/16s and not worry about flex.
you would also have to take into account what the track is like. if it is rough the smaller sidewall of these tyres is going to make it rougher, and it will alter your gearing slightly, since the stock size has a higher profile, at 55.
at the end of the day tyre compund is going to have the biggest affect on grip. if you get a set of hard tyres they won't grip as well as a set of sticky tyres. a set of 195 semi slicks will out perform crappy, hard 245's.