Michael Johnson DL worth adding to roster

I have Jared Allen, Trent Cole, Elvis Dumervil (start 2) would have to drop one for Johnson. Carlos Dunlap available also. Who do you think for the long haul?

Tackles - 1.2
Ass. Tckl- .5
Sack - 7.2 total
TFL - 3
FF - 6
FR - 6
INT - 7
Pass Def - 2
10+ Tckls - 3
2+ Sacks - 3

I'd stay put. Although I really like Dunlap.