I tried with 2 CPUs, E8400 E0 and E7300 M0. Both showed the same strange behaviour (load Vcore 0,1-0,15V above bios setting!) with EIST enabled. C1E enabled gives no problems.
Bios used was shipping bios, which seemed to be newer than the one offered on DFis own website. After I flashed to the bios on the DFI page, the Vdroop control feature was gone, so I re-flashed the other bios (09 something).