I am thinking that the main issue should be keeping the same 5 out there (as best of a chance as they can). IMO Allen just doesn't hold up in those chances. Another issue with Shelton is that IMO we need to look at what circumstances was he out there? Were the rest of the line in tact, was there multiple movements made on the interior of the line?
For the most part when Allen was on the field the other 4 guys were the starting group, how was that in comparison with when Shelton was at C......I know pretty much if he moved from G to C there are 2 movements off the bat......he and the new G.
If it turns out Shelton is worse you go back to Allen.....my point being that we use Allen as the backup...he steps in when needed (if needed).