It's the weight difference. Usually the people who buy RPF1s are buying them for the weight savings. So those people would be even more inclined to drop and inch and a couple more pounds. I mean... c'mon. Unless you step up to the 19s (or bigger if they even make them) and get a brighter finish they are not the prettiest wheel in the world by a long sight.
I said 255/40's for a real stance. 235/40/17's are way smaller in diameter than the stock tires. I've test fit the exact wheel set-up all the way down on BC coilovers with 235/45/17 tires and with more sidewall, they look better. If anything, go with 245/40 tires. Those tire sizes are what people usually run.
Thanks citizenpro!! Your Mazda inspired me to get into one. As far as pricing is concerned, anything over 125 per tire is expensive.....kinda a bummer as they wear out unlike other performance parts