I'm thinking Ivey would be rolling over Stu today.
I've heard a lot of Stuey's friends from back in the day -- Mike Sexton, Billy Baxter, Danny Robison -- say that while Stuey would absolutely love the action available 24/7 today, he most likely wouldn't have adapted to it well enough to play at the level he did then. I'm sure he'd still be a force, but according to them, most likely not to the level of Ivey or Dwan. Especially Ivey who is an all-around great player. Stuey's primary poker game was NLHE and he didn't do well in other poker games
However to a person they all agree that to this day there has never been a better gin player, and probably never will be since gin is almost dead as an action game, compared to Stu's early days. He was a gin machine, virtually unbeatable -- he had to give up so many spots to his opponents just to get them to play, and even with the handicap he just steamrolled everyone.