Posting stable is one thing, getting into windows is quite another and there are many factors you should consider when testing the stability of your system. These are the CPU (naturally), the memory and the actual Northbridge. I have found benchmarks like 3DMark and Sandra insufficient to test a system properly, as I have experience with systems that will 3DMark for hours, but reboot as soon as you do something as mundane as open a spreadsheet. The best combination I have found is to run Sisoft Sandra's burn-in wizard continuously at 100% (low priority) and then start Prime95. If your system is flaky, it will normally produce errors in less than 10 minutes. To test memory I like to use Memtest86, which is a program that runs off a bootable floppy. It has the benefit of allowing you to see how stable your memory is at ridiculous speed and timings without jeopardising your windows installation.
From the CPU point of view, I was able to prime 95 for a few hours without errors at 290MHz (3480MHz CPU). Very nice indeed, however running certain benchmarks (Codecreatures) would cause the system to reboot after a couple of loops. Experience tells me that reboots are normally caused by PSU / memory troubles, where as hard locks are CPU related. Running memtest86 sure enough found 23 errors during test #5 on just the first cycle. Clearly the Corsair is not happy at the 232MHz I was running it at, even though the timings were fairly relaxed (CAS 2.5, 8-4-4).
I backed off the FSB to 280Mhz, and the memory divider to 3:2 allowing the memory to take a sigh of relief (it's now at 186MHz, CAS 2-5-2-2) the system was 100% stable at this speed, running at just under a remarkable 3.4Ghz. 1GHz overclock anyone? =)
