I agree, Voinovich needs to stay in the lineup. Not only to help his development, but also to find out if he can be a point scorer on a contending team going forward.
Personally, I'd like to see Mechler at 157 for the same reasons. That's because there's a possibility (even if remote) that Williams' best weight turns out to be 149. But I can't see John bringing Sheets back and then sitting him.
This team is not in the trophy hunt. And 165 is loaded as others have pointed out. Putting Gfeller at 157 and Sheets at 165 might help with some duals, but it won't make a difference at Nationals. At this point, I think you leave Voinovich at 149, let Gfeller & Sheets rank for 157, and then have the loser challenge at 165 against Harper & company.