bigwhoop,
If you can get the accuracy you desire and about 2850fps in that 22" bbl. You'll have a very good 160 load.
FWIW, I have done much playing with the .280Rem, and this is JME. H4831 is very near an optimal burn rate for maximizing 150s and 154s. The slightly faster R-19 is near perfect for 139s and 140s as is VV-N160. Finally, R-22 has always given me the top end velocity with the 160s and 162s. VV-N165 is right there with R-22, and to boot it does well across the entire wt range. R-22 and VV-N165 give good results across the entire wt range...BUT they are loads at the very top end of pressure according to Quickload...averaging around 65Kpsi. I'm putting 62grs of R-22 behind 140s currently, and even putting mag primers under 61grs. Still it doesn't yeild the velocity that R-19 does with 140s. IME, you have to be very nit-picky, but you can find the perfect marriage of bullet wt and powder burn rate and SAFELY maximize the .280Rem.
The amount of snow on the ground there...is it really cold too? If its in the teens or lower, you can expect your velocity to jump 50-75fps if you shoot that same load in 70+ degree weather. No powder is immune to temp.
You're bumpin' about 50fps per grain...which is normal with these recipes. That should tell you that you might be able to get to 58.5 or MAYBE 59grs. 58.5 should put you around 2800+fps which is good and should be safe too.
If you're going to invest in another pound of powder for the .280...Id stongly suggest R-22, or VV-N165 (which comes in 2lb cans).
Keep us informed
