Senti - how far away are we? I don't think range will matter at least as far as hitting the buildings goes, because Doc has vision magnification and can take aim as a free action. However once moving vehicles, or worse, running people enter the picture Doc will have a very difficult time hitting anything, much less anything at range. Agility 7, non proficiency penalty -1, Smartlink 2, and range of -3 means he'll be rolling 5 dice to hit at extreme range. Even at short range he'll only have 8 dice to hit trained mercenaries.
My guess is that he'll be able to take out the tower, and maybe the first car, but after that it'll be easier just to light up the buildings of the DAWGS from range rather than try and fight using the Gauss rifle.
Thoughts?