I suggest setting your RAM to DDR333 in the BIOS so that you're not overclocking it. Then set the HTT multiplier to 4x.
Then you can play with CPU multiplier and frequency without worrying about your HTT or RAM going over the top.
I lowered my CPU multiplier to 7 and cranked the frequency up to 250mhz (giving me 1ghz HTT back (4x 250)). Then I put the CPU voltage up a bit (no worries about that when you're watercooled
) and got back my 10x multiplier, giving me 2.5ghz. I will play with the RAM speeds and timings at some point too.
edit: Sorry that really WASN'T laymans terms. I'll see if I can grab some photos of my bios tonight or tomorrow for you.