I am using N540 in a 223 with 75 gr. AMax @ 2915 fps and no excessive pressure at all. It performs very well at 500 to 600 yards. Actually N540 is the powder I use the most in sevearl rifles. The 260 with 108 gr. Scenars, the 308 with the 155 Palma bullet.
N550 works great in my 300 WSM
with both 155 and the 175 MK's. And I have just bought some N560 to try in the 260 with the 142 MK's. I really like the N500 series of powders.
Shoot Safe, Shoot Straight.....RiverRat