The higher the power the better, I run 20x50x50 Premier/Leupolds on both my F-Class F/TR guns .308 and .223. The local club shoots 300 F-Class, but I also travel to VT and NH for 600 yd. matches. At 300 I can see my holes so I can adjust if need be, while in VT and NH they have target pits. Look for one at least 40x so you can see your hits and keep your group where you want it. As far as a 20 moa base, you may want to run up to a 35 if the scope you buy doesn't have enough elevation, just in case you get the chance to shoot way out there you'd be set. I have 50 moa in mine, I can zero at 100 yds., and have at lot of room to adjust, more than I would ever be able to use with either caliber.