I've gotten the figures from Webra directly now, and a LOT of help from people in this forum and on the flying field. Everyone states that a cooler plug, a little more nitro and a very much shorter pipe setup will give me the power I need. I'm currently at 58 cm from plug to first baffle on the Hatori 700. Webra say they get 10.400 RPM on a 12x11 and 10.000 with 12,5x11 APC props using the Webra pipe at 49-50 cm and 10% fuel. And I have had several people with Webra's and Hanno's saying that 50 cm is the way to go. Perhaps start a few cm long and work it in a cm at a time.

Thanks SO much to those who've pointed me in the right direction and gotten me the answers I needed. Hope to get to test this new setup this week.