I have both a Century G3 and a Romak III. The Romak has the stock optic, the G3 is topped with a B-square mount and Simmons Aetec 4.5-14x. The G3 has proven much more accurate, producing consistent sub-MOA 100 yard benchrest groups with Federal American Eagle 150 grain ball, and groups between 1 and 2 MOA with most other ammunition. The PSL will run ~2.5 MOA with most surplus ammo, better with the match/sniper stuff (expensive and hard to find).
G3/Cetme 20 round magazines are dirt cheap and widely available, with 30 rounders turning up now and again. The PSL magazines are all 10 round and run about $35.
Ballistics of the two rounds are, of course, virtually identical. For the time being, 7.62x54Rmm is much cheaper, but this will eventually change when the supplies begin to dry up. The 7.64x54 is berdan primed, hence not reloadable. However, teh striations left on cases from the fluted chamber of the G3/Cetme renders brass useless in my experience.
The G-3 is heavier, but more compact. Interestingly, for all it's length, the stock on the PSL is far too short for comfort for the avarage American male. I am in the process of adding a Remington 870 recoil pad to the PSL stock to make it more comfortable. Actual felt recoil is less with the PSL, IMO.
In summary, the G3 is a better Battle rifle and, when equiped with a decent optic, a better DMR as well. But by all means, get the Romak III. For $600, a PSL is a steal (so lokng as the optic is included). I paid $720 for mine, and that was pretty good.