iirc nzxt says the G10 will fit any card as long as it's a reference board, they did not guarantee it will work on non reference card..
that being said, it doesn't mean it wont work on non reference card.. i use the G10 + H75 combo on my non reference 970 and it fits perfectly with no modifications needed (except adding extra heatsink on the VRM)
as for OP, watercooling the card using either G10, Hybrid, or Costum Loop will net you a massive drop in temperature compared to air cooling.. and because the card stays cool, it will stay in boost mode for a much longer period (and in most cases it will stay in that boost clock during gaming sessions).. so even without overclocking you'll get better performance and a much cooler card (pun intended)