A lot depends on how you plan to use the rifle. The 308Win 175gr GMM should be supersonic out to 1000 yds. I personally like a lot of magnification even though it comes at the cost of faster target acquisition. Vortex has a Razor 4.5 x 27 with a tree reticle that works well for me. It's a little heavy but its solid and it holds zero well. I hunt with it and haven't had a problem inside 100 yds shooting deer with the magnification cranked down. I got a 3x15 powered scope for my AR10 and wish I had gone with a higher mag scope.
Go to a shooting range before you buy, and talk to some of the shooters there. At my range, most shooters don't have a problem letting others look thru their scope.
Try to look through a lower 2x7 or even a 3X15 at a target at 500 yds, then look through a 5 x 25...You might change your mind.
Desired magnification is somewhat personal preference so find out yours before you buy. Just my .02
Regards,
M