3500 is on the high end but remember we're talking 30-06 not .308. They are both .30 caliber but the .308 is measured to the bottom on the lands rather than the barrel diameter to denote the different shell casing. The sniper rifles were using the highest capacity casings available with the best load available on 170 grain boattail bullets. The only hotter .30 caliber available was the Weatherby .300 Magnums. (I still have mine.) Each sniper was given 100 rounds at a time and they were hand loaded by some of the best gun smiths in the world.
.308 M59 and M-80 ball ammo is a 150 grain bullet going 2750 Feet Per Second.
Since I'm only punching paper, my favorite for both is the Sierra 168 Grain Match King bullet. I think my speed for both is around 2700 FPS.