I have the 14.25x14.5 OJ on my 05 X2, and absolutely love it. I'm comparing it to a 13.7x17 (had the orig prop, had it re-pitched, then bought a new one), and an acme 14.5x14.25. The repitched 13.7 will be... ok. you won't lose alot off the top end but it'll still be slow out of the hole if you really load it down. After getting the 14.25 it was night and day, I'll throw 800 more lbs than i did with the 13.7 and i'll have to hold back on holeshot (since getting the 14.25 i haven't needed to go WOT, ever). I also have that 14.5 acme, the holeshot is just as amazing, but it spins about 500 rpms more than the acme does at wakeboard speed.
It may be 600, but i bet over the course of a few seasons if you're riding alot like me (150 hrs this year) you'll save at least that much in gas.