It's an ideal muley cartridge. I wouldn't hesitate to run it out to 1k. Any good 130+ grain bullet will do you well. If you're thinking it might be marginal, prepare to be surprised.
I have a 6.5x47 Lapua and have shot several antelope, mulies, and whitetails with it out to 475yds. I use 129gr Accubonds and also 123gr VMAX. The Vmax is maybe not the best bullet for this application but, if you shoot them like a bow shot (broadside double lung shot), it drops in their tracks.
I shoot a 6.5 Creedmoor with the Hornady 143 eld-x and shot a medium sized 4 point Muley at 550 yards in SE Oregon a couple years ago. Complete pass through and the buck went 10 yards.
Have watched a big black bear and a raghorn bull die at over 400 yards with the lapua and rather slow 140 vld bullets. Bull got a broken onside shoulder in the process. Deer are no worries.