I think the more we look at the current selection of weapons, the more we realize there is no unique place for a long-range gauss weapon. We've got plenty.
As far as making such weapons heavy, the best way I can think of is to make the crosshair elastic. That is, small adjustments are slow, but large adjustments, like turning around to face a new threat, can be made at relatively normal speed.
Hell, I wouldn't mind that placed on the micro heavy laser.