I currently have a Vortex Viper PST 4-16 FFP.  This gives me 75 MOA of adjustment.  I'm planning on mounting it to an lr-308 with an 18" black hole weaponry barrel.  Should I get a 0MOA mount(e.g Burris PEPR) or go for the 20MOA mount (e.g. AADMOUNT)?  I guess I'm wondering if I'm wasting my money on a 20MOA mount if 175gr SMKs are going to start going transonic at 700-800 yards anyway?  I'm figuring I might get 2400FPS from Federal Gold Medal loads...

Even when the 175's go transonic, they remain pretty accurate, unlike the 168's.

You may need the 20 MOA mount, you may not. Why not just get it in case? All my precision/AR scope mounts are 20 MOA even though they rarely needed.
I would recommend the AAD mount, ADM mount, and the Nightforce Uni-Mount.

I have an AADMOUNT for a Vortex Razor HD 5-20x50 on a Mega build that I haven't had a chance to get out to the range yet.  However, the AADMOUNT is most definitely a fine piece of hardware.  From a pure craftsmanship perspective, it appears to be well worth the money.

Good advice.  I was mostly concerned if I would be compromising too much when zeroed at 100 yards.  I should still have a fair amount of elevation adjustment left though I think.

I wouldn't worry about that. Most scopes have plenty of travel for a 100yd zero with a 20 MOA base.