I use 58.4 grs of IMR 4320 w/ either a 150 gr Sierra BTSP or Nosler Partition. They are both accurate out to 600 yards but have not tried farther than that. MV is an average of 3140 fps out of a 24" barrel.
Or here are some other options for the 165 grain bullet weights thanks to steves reloading data...
AA-2700 From 59.6 grains to 67.4 grains
Winchester WLR Primer
AA-3100 From 65.0 grains to 69.0 grains
Winchester WLR Primer
AA-4350 From 57.8 grains to 68.5 grains
Winchester WLR Primer
AA-5744 From 27.5 grains to 30.5 grains
Winchester WLR Primer
Big Game From 56.8 grains to 65.0 grains
Winchester WLR Primer
H-380 From 56.3 grains to 64.0 grains
Winchester WLR Primer
H-414 From 56.7 grains to 66.9 grains
Winchester WLR Primer
H-4350 From 57.0 grains to 67.5 grains
Winchester WLR Primer
H-4831 From 63.1 grains to 74.0 grains
Winchester WLR Primer
H-4895 From 51.0 grains to 57.8 grains
Winchester WLR Primer
IMR-4064 From 53.0 grains to 59.5 grains
Winchester WLR Primer
IMR-4320 From 56.0 grains to 60.0 grains
Winchester WLR Primer
IMR-4350 From 58.6 grains to 67.6 grains
Winchester WLR Primer
IMR-4831 From 60.0 grains to 71.0 grains
Winchester WLR Primer
IMR-7828 From 65.2 grains to 74.0 grains
Winchester WLR Primer
MagPro From 67.8 grains to 80.5 grains
Winchester WLR Primer
N-160 From 61.5 grains to 68.2 grains
Winchester WLR Primer
N-550 From 60.5 grains to 64.5 grains
Winchester WLR Primer
N-560 From 63.6 grains to 72.0 grains
Winchester WLR Primer
RL-15 From 54.9 grains to 60.5 grains
Winchester WLR Primer
RL-19 From 61.3 grains to 72.5 grains
Winchester WLR Primer
RL-22 From 63.0 grains to 73.0 grains
Winchester WLR Primer
Varget From 51.3 grains to 59.7 grains
Winchester WLR Primer
W-760 From 57.5 grains to 69.1 grains
Winchester WLR Primer
WXR From 63.0 grains to 72.9 grains
Winchester WLR Primer
Is this a custom or factory rifle 600/900 yds is pretty good distance? I've got a custom 300wsm with a Broughton 5c barrel set up for 165gr bullets and I'd have to think twice at those ranges. Just my .02