You have two real choices in my book.
1). If you're okay with more batteries (like one extra, tops) go fo the Elcan Spectre DR. 1/4x mag with the flip of a switch, ranged reticle/red dot scope all in one. The sight is a bit heavier than the ACOGs but it is rugged and is really able to perform multiple roles on the fly. It mounts to the top of the current issue C7/C8 right out of the box and is a pretty good sight.
The draw back can be too many switches and no HOTAS capability. Remember, fight using your kit not fight with your kit and all that.
2) Any ACOG (I'd pick one with a chevron reticle with fibre optic illumination myself) will be pretty good. A decent unit in 4x magnification is a nice simple, yet effective way to sight in.
No messing about with various settings for various light levels and flipping a lever hoping it ain't one that holds the sight on the rifle. The fibre optic illuminator is self adjusting to the current light level and most of the modles available are NVG compatable.
Keep your stick on the ice, your head up and your ass down. See you on the other side of the spin cycle.