Why would we only keep 2? We have all 4 right now without much issue.
Well, except for getting killed in the paint and losing over and over.
I'm figuring on a center playing the center position, hopefully soon. It would seem that Iverson will be on the squad next year, filling at least the 3rd center spot, and might earn backup minutes.
Olynyk is still a bit of a wildcard. With some conditioning and seasoning on defense, at 7' he could perhaps play C, and surely is expected to be a starter...and fairly soon. That would open up a spot at PF, allowing to keep both Hump and Sully and playing then all a good deal of minutes.
Hump...seems to be a bit of what Kobe once called a MF'er. His advantage in size, and playing bigger than he is, are pretty strong advantages in his favor. I'm a big Sully fan, but I'm not sure how much higher his ceiling might be over his current play, and Hump provides a good deal of that, being perhaps both stead double-double guys. Sully has a better handle and more range, but Hump might run the floor a bit better and be more athletic.
I suppose that I would expect to get more via trade of Sully than trade of Hump, and I like Hump's size, and a rare combination of professionalism and MF'erness. That's why I, and I might be in a lonely group here, would keep Hump and look to move Sully as a deal-sweetener for a talent upgrade elsewhere, e.g. backup PG, starting SG.