It will likely make no difference either way. The 6700K will happily run at 80c+ for decades with no ill effects, and nVidia designed the 980 Ti with a load temperature of around 85c in mind. Cooling these chips down further has no practical benefits, though I could see noise reduction as a worthy pursuit.
For what it's worth though, the 980Ti will draw more power, and thus will need more heat dissipated.