Problems running 4 dimms in K8 Neo2 Platy...

I'm trying to run 4 dimms in my Neo2 Platy. all are Mushkin 2 are 512mb(ch5) 2 are 256mb(bh5) I'm can't get it stable unless I run below 200mhz. I've bump the Vdimm up to 2.85. I can run this exact dimm set up in my Nforce 4 board and runs well at 224 @2,3,7,2. but not on my Platy. Any suggestion?

Thanks,
PWA