Sirex sorry for my eariler post. Did not mean to go off topic, but the man asked, so I answered. Thats a beautiful plane you have there. Those SPE40 engines are sweet. I really like mine I would go with a different prop though. I have found the best static thrust on the 21X8 Xoar. I have tried ProZinger 20X8, Mens Ultra 20X10, and the Xoar. As far as balance goes try moving the ballast as far from CG as possible. The further from CG the less you will need. You have probably already heard of these, but incase you have not here is a link.
http://www2.towerhobbies.com/cgi-bin...&I=LXK246&P=ML
Bob