FWIW - my limited experience with PSL's leads me to think you'll be disappointed in the PSL's effectiveness as a "600-800 yard" rifle. Last year a buddy and I bought a PSL-54C each, from AIM, along with a case of Polish ammo (early 1950's vintage if I recall). The rifles had awful triggers and the groups were awful also. With new triggers, and after trying a variety of ammo (always light ball), off the bench my rifle will hold a 3" group at 100 yards with Czech light ball, my buddy's will hold a 2.5" group, same distance and ammo.
These are three shot group only with time between strings to allow for the barrel to cool. As the barrels on our rifles heat up they string shots vertically.
Both rifles function fine, are fun, and cheap to shoot but don't quite cut it in the accuracy department. I suspect there may be ways to tweak the rifles some, and if you handloaded some precise ammo, or could find (and afford) some Russian 7N1 ammo, I think group size could be shrunk - how much I don't know. Part of my disapointment with the rifles is, I realize, unrealistic expectations on my part, and to be fair others have reported getting excellent groups from their PSL's.