I wish I could find the story on the web, but this information comes from the Insider pages in ESPN the Magazine. You could probably just grab one while in the store and just find to the back of the magazine under the NFL page in the Insider section. At the bottom of the page is a short article about true value and how the top 3 Center FA (Brown, Grove, and Birk) are worth the money they got in FA.
At the very end was a stat I found very interesting. It discussed the percentage of time that each Center went one on one with defenders. Now it doesn't state whether a RB/TE counts as help in a one on one situation, but I think for the sake of argument, we can say one on one means they were on an island without possible help from any other player. Here is how the percentages boiled down:
Grove - 67.5%
Brown - 60.3%
Birk - 39.9%
I was a little shocked at the disparity between Birk and the other two. Birk got assisted on 20% more plays than the next closest guy and almost 30% then the top guy. I would have thought that Birk would have a % much closer to the other two players, but according to this is seems like 60% of the time (it works every time ;) couldn't resist) Birk had one of the two OG's or another player helping him with a block.
If that same scheme is played with Sullivan (where he is one on one 40% of the plays and has help 60%), I am pretty cool with that. Even if it were a 30-70 split or something along those lines, I don't see too bad of a dip in production. Also, if it were some how that, the reason Birk had help on 60% of last years plays, was because he was the one doing the helping, I think Sullivan could do just fine in that role too because if there wasn't much of a need to have Birk going one on one a lot, then there probably won't be a big need to have Sullivan going one on one right away either.