What engine? MCX? I think the 08 MCX X2's came with a 15.5" pitch prop. It will be lacking some at altitude. Not as bad as the 17 pitch on my 06 X2 though. That thing lost alomst 1000rpms at 6500-7000'. I propped down to a 14.5x14.25 ACME and the difference was night and day. Good hole shot now, got all my rpms back and still get 41-42mph on flat water.
Other than that it will run fine at altitude.
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN