Both Jay Ratliff & Tank Johnson are 6-4, 6-3, & weigh around 300 lbs. That is DE size in a 3-4 scheme. Either may stand up to constant double teams for a little while, but eventually will wear down.
The smallest NT in the NFL NOT playing for Dallas used to be our NT--Jason Ferguson of the Dolphins. Jay is 6-3, 305. He does alright, but has a totally different build than Jay Ratliff.
Bringing in a 310-320 lb. nose tackle would allow Ratliff to move to his more natural spot at DE, where he would be able to beat single blocking and get more sacks. He is one of the best sack artists at nose tackle in the league. Just think what he could do at DE.
We would then have a player who could withstand the beating at nose tackle with more size in one of the free agent NTs in the off season.