I would suggest saving more money if you would like to hit at 600 yards. 600 yards is pushing it for high-end thermal equipment besides clip-ons.
The XM30 is native 3.5 magnification with 320px. So at 7x you're at 160px. 160px is pretty hard to recognize anything past 300-400 yards. So how can you be sure what you're even shooting at?
Either save more money for a NVision Halo LR or a Trijicon Reap with 4.5 native mag. Still not sure about any 600 yard shots.
If that's completely no go due to $$, get the bering optics super hogster.
If you're dead set on the thermion, save for the XM50.