You will get between 9700 and 10100 on an apc 15X8 prop. I usually got mine to about 9800. This is almost identical to what the 110FZ puts out, whic is the ultimate engine choice for the funtana. However, many people claim the need for more weight up front, so your 120 os a good choice...you will want to run an apc16X6. BTW, this is the same engine that Kyle used in his video. If you haven't seen it, here's a link...
http://www.kyle.macapple.com/Videos/...ueen-small.wmv
BTW, he said he thinks it's a 120FZ. Nonetheless, if you keep it under 9.5lbs you'll be fine.