Nitro works in WGs so stick with Nitro.
But if you head over to the forums, the WS-66 is out now and it looks like its ALOT cooler. Id go with the 66 RIS over the 65 if I were you. I just bought my 65 and now I want the 66 real bad lol, dont make the same mistake
look over both guns before you buy, 65 has sidecocking and a smooth barrel.
66 has a better looking reciever, the stock and barrel are using pins instead of threads so they stay straight
the barrel is rifled
top cocking (M16 style)
no external parts move when its shot
and the barrel isnt spiral rifled, its straight, 3 grooves o nthe top, which adds LOTS of distance, but its better than the Flatline which slows down paintballs miserably.