vCore, vNB, vFSB - Any way to know which one to increase?

[blunden]

I've been running my Q6600 at 400x8, 1.328v idle, 1.312-1.328v load for some time now. Seems to work great (Prime95 for a couple of hours). However, I now have some free time that I thought I might use to improve that OC a little. The specs (bought at the end of last year) are as follows.

CPU: Q6600 G0 L726A951 (VID: 1.2875v)
CPU-Cooler: TRUE + Scythe S-flex 1600rpm @ 1300 rpm
Mobo: Gigabyte P35-DS4 rev. 1.1 BIOS: F12
Ram: Corsair TwinX XMS2 CL5 2x1GB + OCZ 2x2GB 800MHz (OCZ2N800SR4GK) @2.1v
Case: Antec P180 (first revision)
PSU: Corsair 620HX

Currently every voltage except vcore and vMem is standard. Is there any way to know if it's vcore that is stopping me or if it may be vFSB or vNB? Are there any guidlines I might have missed when it comes to the voltages other than vcore in regards to overclocking?

I know 4 memory sticks tax the NB/MCH more but it's been working at standard vNB without a hitch since I bought the extra ram.

[blunden]

I keep getting a Rounding error in Prime95 pretty quick @400x9, even at 1.424-1.440V vcore. Doesn't seem to make any difference increasing vcore. Does that mean it might be vNB or vFSB, or does it simply mean that even more vcore is needed?

[Hyperhorn]

If you just raise up the CPU-multiplier you don't need more vNB oder vFSB. But not all Q6600 can handle 3.6 Ghz on air. A friend of mine had a Q6600 which wasn't primestable at 3.5 Ghz @1.42V, so it depends on your CPU. (And don't forget: No one likes to share crappy results, so the normal results for a certain CPU regularly are worser than shown at forums)
But you can test your maximum following:
Try for example 420*7, then 440*7 and so on, but don't step over the known primestable CPU clock. I'm pretty sure you need at first some extra vNB and then when you arrive FSB Wall some extra vFSB.
Then decide what you like for 24/7. Maybe 440*8 is better for you than 400*9, even if CPU clock is 80 Mhz lower (just an example of course, it depends on your memory, too etc. )
+0.1V vNB is okay, but more than +0.1V vFSB is not useful for 24/7 IMO

[blunden]

If you just raise up the CPU-multiplier you don't need more vNB oder vFSB. But not all Q6600 can handle 3.6 Ghz on air. A friend of mine had a Q6600 which wasn't primestable at 3.5 Ghz @1.42V, so it depends on your CPU. (And don't forget: No one likes to share crappy results, so the normal results for a certain CPU regularly are worser than shown at forums)
But you can test your maximum following:
Try for example 420*7, then 440*7 and so on, but don't step over the known primestable CPU clock. I'm pretty sure you need at first some extra vNB and then when you arrive FSB Wall some extra vFSB.
Then decide what you like for 24/7. Maybe 440*8 is better for you than 400*9, even if CPU clock is 80 Mhz lower (just an example of course, it depends on your memory, too etc. )
+0.1V vNB is okay, but more than +0.1V vFSB is not useful for 24/7 IMO

That's what I thought since the FSB was constant and I assumed vFSB would only increase max FSB a little. I backed down again now. Maybe I will try again later when I feel like it. But in general, increased vFSB and/or vNB can only increase stable FSB, right?

Maybe I will try bumping up the FSB some more or tweak NB performace level or memory timings. I'm guessing some more vNB might be needed when overclocking the ram since I'm using 4 sticks. I guess this is what you risk when buying the CPU relatively early. All things aside though, running it at 400x8 is actually enough since my GPU is probably more limiting in gaming anyway and I always seem to have enough CPU-power whatever I do. It's just that having a little overclocking project is fun.

[Hyperhorn]

But in general, increased vFSB and/or vNB can only increase stable FSB, right?

I never found out anything else. If your system works correctly, answer is "Yes".
Maybe your CPU gets to hot, many Q6600 @air are limited by core temperature and no by max. FSB.

[blunden]

I never found out anything else. If your system works correctly, answer is "Yes".
Maybe your CPU gets to hot, many Q6600 @air are limited by core temperature and no by max. FSB.

If it was a temp issue shouldn't I at least see a very high temp in CoreTemp or RealTemp before it errors in prime95? I crashes before I even reach 60-65 degrees in CoreTemp @ TjMax = 100. I temps like that or slightly higher when priming for a few hours @ 3.2 GHz when my ambient gets high (up to 28 C) without a problem. Strange.