You're gonna love this plane, I've got a YS45/tuned pipe on mine & it's the fastest thing I've flown yet. Some guys down at the field are calling it the missle now. I found this dopler shift program here on RCU, it measures the sound on a high speed pass & comes out with mph & rpm. do'nt know how accurate it is but I'm a little skeptical on my numbers. Prop used was an APC 9x9 peaked @ 16200 rpm on the ground.
Temp....60 degrees
wind.....10 mph gusting to 20 mph
Upwind....121 mph @ 17385 rpm
Downwind...134 mph @ 17621 rpm
Down wind...146 mph @ 17829 rpm
I know I'm doing 100+ but that 146 sounds unrealistic, this program should help in selecting the fastest prop though.
Here's the links if you're interested.
http://www.philsrcworld.fsnet.co.uk/
http://www.alphalink.com.au/~hughan/frames.html