More than that ,15-20% i guess. From what i know E8400 and E5200 have the same core, 45nm, Intel virtualiztion E5200 does'nt have.
The main diference is the cache which is 6mb for E8xxx and 2mb for E5200/
Anyway this E5200 do a great concurence to E7xxx, and smash with al x2 series from Amd up to X2 6400, an even to triple core
It's seems that Intel realy wants to crush Amd