Agree with the preceding points. The typical recommended powders lie in the IMR 4350 to IMR 7828 range. I've been doing a little playing with QuickLoad for my 6.5x55 and have found that exceptional velocities at acceptable pressures are possible with the newer Alliant Re26 powder. The same velocity gains with this powder as in the .270 Win. In fact, the 6.5x55 really approaches .270 Win. power territory with Re26. QL gives 3000 fps at safe 60,000 psi pressure for the 130-grain Nosler Accubond bullet out of my 23.5” barrel.
When sighted to hit 3.0” high at 100 yards (my usual sighting practice for long-range hunting), the 130-gr. .270 Nosler Accubond with MV of 3100 fps is down 11.8” at 400 yards, arriving at that distance with 1478 ft. lbs. of energy. The 6.5x55 with the 130-gr. Nosler Accubond LR with a MV of 3000 fps sighted the same way is down 12.2” at 400 yards (so only .4” below the .270), but arrives at 400 yards with 1548 ft. lbs. of energy and with a superior sectional density of .266 vs. the .270’s .242. So the actual killing power of the 6.5x55 is superior to that of the .270 Win. at that range, both with 130-gr. bullets—what I’d consider the ideal weight for deer-size game.