P5N32-SLI Premium 4gb Memory issues

Just upgraded from 2gb to 4gb 667mhz memory and my system is so slow.
My motherboard is an Asus P5N32-SLI Premium, all my sticks of memory are the same. I read a post that had the same problem be he had an ASUS P5N32-SLI SE Deluxe mobo. He solved the problem by enabling memory remapping in the bios, I can't find this option in my bios and I'm a little relunctant to change any other setting as I don't really know what they do.

Can anyone with a little more knowledge help me solve the problem

Thanks

Do you suspect one of the new sticks are bad?

Do they all pass memtest 86+?

What are the times on those new sticks? Are they the same times as your old ones?

the new sticks are good if I try them in pairs they are sweet its just when all 4 are put together I cant see the memory remapping option in the bios might it be called something else??

All the sticks are exactly the same