7x is plenty for good shooting with a big game rifle at 300 yards. For range testing it really helps to make a target that is easy to line up with the reticle/magnification/distance combination in play.
With a correctly proportioned target I've shot well below moa at 300 yards with a scope whose actual magnification tops out at 3.9x. The little straight tube Leupold looks kind of funny sitting on a rifle sporting a 27" #7 contour barrel, but the combination does make a point at the range when I'm talking to folks who think you need 14x or more to take deer at 300 yards.
