Had 2 mates that built their 6's at the same time. One went the metal constant speed prop and the other a 2 blade timber. You could hardly suggest that one was faster than the other. It was an interesting comparison.
Have another mate put a 3 blade constant speed on his 6 and found it went a bit slower, but was noticeably smoother and more comfortable and a little quieter.
Both of them were a 150 knot TAS machine up high in the 7,500ft+ range.
One of the guys I know took his 6 up to New Guinea and Vanuatu, 160hp C/S, that thing would still climb at close to 1,000 fpm at 12,000 ft.
The 6 does have a tendency to fish-tail (yawing) at high speed when you are pushing it whereas the 7 doesn't. Even the 10 does this when pushed.
Great performers.
Suggest the Van's Airforce forum for more info on the RV and maybe a trip to OshKosh this year.