I use N550 for one of my favourite loads for my beloved .270 Win.:
130 grs. Nosler Partition, 55,8 grs. N550, Fed. GM 210 M, OAL = 3,28", Vel. = 3130 fps., accuracy is 0,59"(5 shots).
Never had any pressure signs in my rifle (Steyr PH)but start lower and work up.
I started at 55 grains with the NP as well. Now all I need is a break so I can get in some range time........
I'll post the results when I get 'em.