I am also curious about N540. It has been a great powder for me in 223, using the 80 ELD and running them long - 2.50", 2880 out of a 26" Krieger
Anyone try N133? It's THE powder for the benchrest guys in 6PPC, but they run lighter bullets. I've used it with 77s in 223 and while you can probably get higher velocities with other powders, the SDs are single digit.