Re: remington 700 sps tactical
you're off to a good start here, and assuming the rifle shoots accurately to start with, should do you fine for some time to come. As far as the effective range question, that's a bit subjective. The 308 is very widely used as a 1,000 yard target cartridge, but those are specialty rifles built just for that purpose; very specific throating, specialized chambers and bullets matched to this type of shooting. With a standard off-the-rack rifle, given some good long range ammo like the M118LR or a commercial equivalent, I'd say 700-800 yards shouldn't be out of reach, assuming you're willing got put in the trigger time.
I'f you're handloading already, you can get a head start here by selecting bullets that are suitable for these distances, basically a 175 grain and up. Don't hesitate to ask questions here, and you'll find more than a few answers to ponder. Welcome to the site!