The 62k NATO pressure is widely misunderstood, and highly dependent upon chamber design. See below:
http://www.m4carbine.net/showthread.php?t=55149
All things being equal, I'd recommend 55K max for no other reason than pressures above
that (from my experience) begin to stress primer pockets after a few (5-6) firings.
Besides (as noted in the previous post) it isn't needed to reach military-matching ballistics.)
