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Did you read the thread befoe asking this question?

Memory choice is all about how hard you want to overclock and how good is your CPU and whether you are really bothered or not about a second or 2 on superpi 1MB test. If you are not overclocking then DDR2 6400 memory will meet your requirements. No need to buy higher spec if you are not going to use its full capabilities.
lHigher FSB will give you higher bus speed and and run the memory to its best capability at 1:1 . If you run a q6600 say at 450x8 (or 9 if you are so lucky) then running DDR800 memory slightly o/c to DDR900 with tight timming will give good performance/speed. That said I have Ballistix 1066 memory that I run at 1128 on good timming to get a slightly higher bandwidth -depends on what you are looking for. If you run FSB above 450 your 6400 memory may not be capable of o/c to run 1:1 opr higher so you get 1066 memory - its all so cheap now why not just get the 1066 which you know is going to clock higher than the 6400 mermory. If its good quality o/c chips it will also run tight timmings at lower speeds.
Check the article I posted in a previus post re the techrepository o/c quide . It gives a detailed expanation on maximising FSB/BUS etc and a o/c speadsheet where you cen see what the actual speed /CAS response gains would be or not.

wonder if a zalmen 9700 ultra quite would do well at 3.6 .

Iy should be good for that - its a good HSF. Not as good as the thermalright 120 extreme or the ultima with good fans but good enough to o/c the q6600 to 3.6 .

Thanks, this timing and clock speed stuff is a new concept to me.

It looks like detailed explanations have been given already, so I will throw my vote in for DDR2-800. There's no practical need for DDR2-1066, even when overclocking.

If you want 3.6GHz (unlikely unless you get a GREAT G0 stepping) you will need an FSB speed of 400MHz. This equates to DDR2-800 at a 1:1 ratio.

Realistically you will need to lower the multiplier on your Q6600 to 8 for a final clockspeed of 3.2GHz. Don't sweat it, you'll never be able to tell the difference.

A lot of q6600 GO reach 3.6 or more on air with relatively low volts. The latest batches with VID of 1.2 are getting even higher on air- with water 4.0Ghz plus. . The one I have will run 3.8 (475x8)3dmark06 stable on 1.45v but not prime. So if you run a lower multiplier and can run higher FSB (say anything above 450 upward) you may be better with 1066 ram to run 1:1 cos not all 6400 ram o/c that well. 8500s will also give you a more or less guaranteed option of o/c to running on higher ratios e.g 2:3/4:5 etc to gain higher bandwidth. If you dont want to push it hard then buy good 6400 RAM like ballistix and its no problem - 8500 are after all only cherry picked 6400 chips in alot of cases..

Okay, maybe the G0 steppings are better than I thought they were. I still don't think a FSB of over 400MHz is necessary. Seriously, can you really tell the difference between 3.6 and 3.8GHz?

As a side note, I just realized that it is incorrect to say "an FSB." It sounds wierd, but it should be "a FSB." I won't be going back and editing my posts though

Any ncreases makes a difference to scores in Superpi and 3dmark etc which are important to overclockers trying to get highest scores and squeezing the last out of the system or just the fun of seeing what it can be pushed to as a rule. The system performance on mine is a lot zippier and responsive with 3.8 - faster bus speed ,memory running slightly higher etc. unfortunately not fully stable though -lol!. So I run 3.6 quite happily 24/7 and its pretty good for all games out at full maxed settings(except crysis which eats PCs) - I have a decent graphic card which helps a lot as games now tend to be re GPU restricted . At 3.6 itw great for video editing, Burning CD performance etc. So unless your in it to see what you can get it maxed to stable - 3.6 is great.

If you havent read it already check this overclocking guide for optimum performance setting re what you actually gain or dont from increasing FSB etc. http://www.thetechrepository.com/showthread.php?t=195
Very interesting and informative

Guys, if I may ask, how does ram mhz effect cpu overclocking? I'm planning to get an Q6600 as well and overclocking to 3.0, and I didn't know that I have to pick the rams carefully until now.

Normally it is best to run the ram @ 1:1 timings with the cpu.

So even a Q6600 @ 3.0 only needs ram that runs at 667.

Thats why many say just get 800.

You can even drop the multiplier 1 notch and run 3.2 @ 800...

For extreme memory over clocking you can drop the multi further...so you get moderate CPU speeds(still over 3.0 and fast ram)

@ sesdave: So in gaming and every day use you can really tell the difference between 3.6 and 3.8GHz? I don't have the right to doubt you because I have never even seen a Q6600, much less been able to use one, but jeez that's hard to believe. I can't even tell the difference between 2.0 and 2.5GHz on my x2 3800+ unless I'm benching.

Not quite - I said the PC seemed zippier. I was refering to the operating system(I run Vista x64 so I need all the help I can get-lol) You get slight increases in benches etc but no real gain in games and real day apps. Thats mainly due to the fact the are not optimised to use mutithreading. The only real advantage a Q6600 give you over dual core at present is improved scores on 3dmark06 and times on video rendering and burning CD. But the are the furture as games and apps will be moving in the direction of multithreading. But they are cheap and overlcok relatively easily with a decent motherboard. But that said penryn,x48 and DDR3 are round the corner. Another expensive adventure for no real purpose apart from fun - its as bad as when I used to play with cars to make them go faster and look flashier- lol!

Ok, help! Im on a 680i and i have the ultra tec cooling system, but for the life of me i cant get any better than 315, not even 315.25 ( vista doesnt even start then) and a stable one of 305 resulting in a horrible OC of 2.745 MAX.

Now, I haven't messed with any voltages as im not sure whats safe and how they effect the clocking ability. Am I doing something wrong or did i just get a complete dud?