If you can see a 1 MOA (1") dot at 100 yards with any given optic, you can see a 1 MOA (6") dot at 600 with no issue. So, if you're capable of holding on a 1" target at 100 yards with the scope then you're perfectly capable of holding on a 6" aiming point at 600 yards, which is well within the kill zone of a deer. I typically shoot my optics on a relatively low power, 12-14x is about perfect. I've done a lot of shooting at 1 mile with a Sightron S-III 3.5-10x44 and I've never felt handicapped.
I think the only issue you're going to have with that scope will be compensating for your drops at 600 yards. Instead of changing the turret though, maybe think about changing the reticle to something like the Boone & Crockett reticle. In a 338 Win Mag, I'd expect a bullet like the 225 Accubond to get you somewhere around 2750 fps from a 24" barrel which would match up pretty well with a lot of the drop compensating reticles out there. With a little practice you can figure out where your specific loads will impact at give ranges using the reticle and it makes it a little easier than twisting turrets. Also, some of the older VariX scopes just don't track well and you end up having problems when you spin the turrets too often.
For the record, I think the 338 Win Mag is a great LR chambering with the right load. I'd stick with bullets in the 225-250gr range and you're good to go out to 600 yards with no problem. Just put in the time practicing and you'll be fine.
