After all my test I was still curios to find out how much rpm I would get with a small 3cell lipo battery on the original setup. Last week a small size 3cell 850mah lipo battery from hobbyking arrived.
The result on the original setup: > 17000 rpm @ 11.45v !!!
due to the lack of time, no video this time :)
conclusion: If you are not into rebuilding the original setup of this plane I advice to equip this rc model with a 3cell lipo battery (11.1v) and not a 7.2v Nimh/lipo battery as indicated in the manual.