As nice as the G1 is, you'll always be overclock limited by the temperature which will throttle the card long before you are by the card itself. If you are spending £650 on a GTX980Ti the hydro is a much better option if you have a place to put the water cooler unit.
That is of course assuming you can actually get one.
Looking at the G1 temps in reviews its so far away from peak TDP that it throttling wont be an issue.
Heck of a cooler on it.