Consider 4000 yards for Romo to be a solid season. In his stellar 2007 year where he broke a lot of records he threw for 4200. Take that 4000 and break it up between the WRs, TEs, and backs. Let's ignore the fact that Dallas will probably lean more heavily on the running game this season, making 4000 a little iffy...
Figure that Roy Williams has a decent year at 1000 yards. Optimistic? Maybe. If he really clicks with Romo, it could be more.
Look at Witten, who is obviously the dominant tight end in the game now. Does he get close to 1000 yards? With less confidence in the WRs, maybe. In 2007 he was around 1150. Last year he was at 950. Does he lose catches to Bennett? Does he pick up catches that were going to the WRs? Call it a wash.
So there's half your projected yardage gone. 2000 left to work with.
Crayton? In 2007 he was at 700. In 2008, he went for 550. If he's truly going to be the #2 receiver, odds are he comes closer to the 700 number.
Throw in Miles Austin and Sam Hurd. Do they get 300 each? Hurd had 300 last year. Austin had 300 the year before. I think this is one of the two biggest factors - how often do they have one or both of these guys on the field instead of a second TE?
The last factor is RB receiving yardage. They may decide that Felix needs 30 catches or more. Barber may get fewer than years past. If Garrett wants to get the backs more involved in the passing game to cut down on Romo's mistakes (and to take advantage of Felix), that's going to cut into Bennett's numbers. 250-400 yards for Barber and somewhere in that spectrum for Felix makes it dicey. I'll leave out Choice just because it seems like they'll have to force him in for a series or two since the team is so loaded at RB.
Adding those numbers up, I'd be inclined to take the under. Of course a Witten injury and/or hits at the #2/#3/#4 WR postions makes the over much more enticing. Garrett getting totally pass happy will help, especially if Romo can eclipse 4500 yards. That doesn't seem likely though since Garrett going that heavy on passing probably dooms Dallas to a bad season. They have to run to be successful in my opinion. Jerry may be putting post-it notes on the coaches' desks saying just that.
Here's the real splash of cold water for you: A 500 yard season would put Bennett at #16 in receiving yards for TEs based on 2008 stats. (
http://www.nfl.com/stats/categorystats?season=2008&seasonType=REG&d-447263-o=2&statisticPositionCategory=TIGHT_END&tabSeq=1&d-447263-p=1&d-447263-s=RECEIVING_YARDS&d-447263-n=1) That means Dallas' SECOND tight end would have more yards than half of the league's STARTING tight ends. Unless you are looking at a team like Chicago or Miami last year with no WRs (and neither of them pulled off that feat), I'm not confident. I'm too lazy and it's too late in the evening to do the research, but how many teams have ever had 2 TEs go over 500 yards receiving?
I'd hedge toward the under.