I checked with my Burris Tech Rep on this and he replied:
"Funny enough, 6ARC gas guns are what we have been using ourselves- the flatter trajectory and longer, heavier bullets offer better inflight and terminal ballistic performance, allowing our shots to be less sensitive to ranging errors at night and without LRF capabilities (which can be enhanced with a weapon-mounted LRF, as some of the others in the thread have mentioned). While I can’t speak very well to the performance of rifle-mounted image intensifiers(I2) such as the PVS 24/30 LR, we do have plenty of experience with our line of thermal clip-ons. The BTC’s return to zero quite well, so when we’re sighted in at 250y with 75gr VMAX projectiles going 3k fps at the muzzle, we’re able to get ±~2.5” of the crosshair out to 300y, and not a ton of drop out to 400y, so it works out pretty well.
I’d say Pro’s are: target detection with thermal is far better than either Digital or I2 NV devices, and ideal magnification range for our thermal clip-on is between 2-5x, so OP’s 4-16x should work fine. Con’s are that image quality is not as good as NV, and his Nightforce’s reticle will be quite small at low power if it’s FFP, so I’d hope that he’s got reticle illumination to help out with that."