Which ceiling are you talking about?
Are you talking about wins, stats or pro potential?
As far as wins - I think yes; I don't see how he can lead his team to 9 wins next year.
Stats - I think yes; I don't see how he eclipses the numbers from last year while losing some pretty decent WR's and replacing them with more physical, slower WR's.
Pro Potential - No, I think he can have a solid year this year and make himself draft eligible if y'all run more under center plays and develop a more pro-style attack. I don't think that gives you the best chance to win games, but I think its the best chance for Russell to get drafted.
I don't know what Tyler Bray's draft projection is, but in my opinion Russell has a better pro skill set than Bray. He stays in the pocket, has a strong arm, is fairly accurate and has solid pocket presence. He also adjusts well based on defensive scheme. With his height and arm, I think he is a perfect fit for a pro style offense.
Honestly, if he had been the QB at LSU last year I think they win the National Title. I also think his numbers would be really good and he would a 1st-3rd round pick depending on how the season progresses.