I also think you're substantially overestimating the RV speeds - the ones I've flown in (or next to) are not as fast as you're listing.
All my $0.02 :-).
A lot of it is about engine choice. My 160 hp RV-6 can cruise at 190 mph, but I'm generally running 60-65% and 175 mph. The skinnier airplanes and the ones with more HP go a bit faster. The ones with poor attention to detail go slower. That's for sure.