Groves uses his speed and relative slickness to get a UD. In fact judging by how Froch was able to land on and hurt Kessler, I wouldn't be surprised if Groves stopped him at this point in time.
At the very top level Kessler, like Froch, is slow, robotic, predictable, limited and easy to hit. Groves has the style to outclass Kessler pretty easily and stop him, but of course Kessler has a punchers chance.
Haye said he watches Groves outclass Kessler in the build up to the Froch vs Kessler 2 and that was before the fight.
There was rumours that Groves had bashed Kessler up in sparring at that to the now probably slightly more attack minded Groves id expect a knockout in favour of GG. I like Kessler, and think the Kessler of 3-5 years ago was a brute, but the 32-33 year old Kessler is a shadow of his former self. Groves would destroy him