rule of thumb I go by is anything over 10x an AO is a good thing.

I think most rifle scopes parrallax is set to 150yds.....so out to 200yds I think everythigns good, but once you start looking at 300, 400, 500yds, not being able to aadjust for it could cost you.

I have a vx-iii 4.5-14x40, and a x50, both are long range models, LR, 30mm tubes, with the side focus rather than the AO, very nice/handy, think about it....