I think the limit is 15turn
why not look at
http://www.oople.com/forums/showthread.php?t=17331
Model Images posting, MRT pro esc's are no limit, motor wise, and 11x2 or 10x2 motors were £65+ new, you will need to have and be able to use a chunky soldering iron, possibly change your battery connectors, add power caps & diode and possibly look at gearing.
MRT instructions =
http://www.team-mrt.com/pdf/vxpro.pdf
the 7x2 would be bloody stupid fast, and strip the gears out of your diffs.
Find a club that races buggy's localy, best advice.