I used a 16" MR308A3 at PRS once. The farthest shot I was able to connect at PRS was at 604m with IMI 175 SMK, on a 12" plate. Maybe that is why HK advertises G28 as effective out to 600m. haha
YMMV, my opinion is that, yes, at PRS ( not at KD square range with a spotter ) with good fundamentals, good data and some good wind reading (with cooperating environmental factors) IPSC size target should not be unachievable out to 700m, but from 700 to 800 the bullet starts getting tired and the drop is getting bigger. It is still pretty doable because people have done it quite often, but i won't say it is a newbie shot. Getting the right ballistics numbers and solid wind dials are more of an operator skill thing, as well as knowing the ammo and the gun at the ranges being used. .
IMHO, shooting a MR308A3 16" in the tactical class of PRS is not exactly the winning move. It is a 1MOA gun, the people shooting sub MOA guns at higher velocity and therefore lower BC and lower wind deflection will always have easier lives.