Mixing RAM speeds

right now in my computer i have 2 sticks of Crucial Ballistix DDR2 1066 http://www.newegg.com/Product/Product.aspx?Item=N82E16820148069 , i know its overkill for my system (Q6600), but i got it $70 off which brought it to the same price as the slower ones, but now i am interested in buying 2 gb more, but dont want to pay the full price for another set. so what i want to know is if i can buy some cheaper 800mhz ram and put it in there with the sticks that i have now. i will probably buy crucial again

and im aware that i need a 64 bit OS

if i need to, i can underclock my memory right?

Yep, underclocking should be fine. Basically if you do that you should think of your 1066 ram as 800 ram - just act as if you had four sticks of 800 and be aware any overclocks will be limited by the slower RAM.

--Illah

What speed are you running your RAM now? Be aware that running 4 sticks puts a lot of added stress on your MoBo. What are you doing that requires the extra RAM?

True, more sticks makes memory control more difficult so that will affect your ability to tighten timings and whatnot. The severity of the effects vary though, depending on your setup it could be small.

I actually just went to four sticks from two. It's a DDR1 setup and it cost me 10MHz on the RAM overclock with the same super-tight timings (2-2-2-5). Overall that loss amounts to a 4.44% loss in speeds which is nothing I'd really notice in real-world apps, and the extra GB of RAM more than makes up for it.

Strangely enough Memtest reports my RAM bandwidth as being higher despite the lower speeds...maybe because I'm now running dual dual-channel? So maybe in a sense I lost MHz but not actual speed

--Illah