If he does move as high as 172, which is what it would take to get a fight with Ward, I think Chunky would be a good litmus test. If he could easily handle DeGale, or possibly stop someone like Bika.....I think a fight with Ward at 172 would be very winnable for GGG.
No use suggesting who we would want to see GGG fight. He'll never face those we want him to like Lara. Instead he'll wine about being ducked and announce he's fighting some featherweight moving up to 160.