Autotune is junk - it never gets it right! I ran autotune and ages later it settled on 915 for the core and 1117 for the mem I think but it wasn't stable at those speeds. The mem could do more, the core less.
Oh, the X-Fi - what an adventure, soon you'll wish you didn't ask!
*DEEP BREATH*
My X-Fi is back in - it wasn't the cause, although with it in the symptoms were worse. Without the card the random hanging in Windows and post problems resurfaced if I tried to overclock the motherboard. It was difficult to diagnose because if a hang happened, I had to switch my PC off for at least an hour to regain stability or strange things would happen like drives not getting detected, system pausing and hanging, hanging on post, keyboard going missing - even if I yanked the plug and cleared the CMOS! Leave the PC for an hour disconnected from the mains and it was back to normal!
With my old 4850, I could clock my MSI P45 motherboard to 400 FSB and run the E6850 at 3.6Ghz at 1.3425v. Then I put in a GTX 280, and immediately had to run the E6850 at 1.3625v, probably because vdrop (voltage drop) was a lot worse with the GTX 280. This hints at a PSU limitation.
Well, with the 5830, a much less power hungry card, I was having issues overcloking the board at all without crazy stuff happening. Everything back to default and the machine left for an hour and it ran 100% stable. Then I found an option in the bios to only set overclock settings after Windows has loaded - so at post it fires up with default settings.
This fixed everything, and amazingly I can run my E6850 at 3.6GHz with a much lower voltage - 1.325 - the default for core2 duo's - plus all the energy saving options (changing clocks and voltages) left on. I have tested it running prime, games, benchmark all at the same time. Solid as a rock.
So what was the issue? My guess is the 5830 required more startup juice and caused greater variance in voltages than the other cards and my PSU was struggling to meet all the required voltages. But once past post, the most strenuous time for voltage drop as everything demands power at the same time, the PSU can handle everything fine. If I'd found that setting earlier, I could have been running this E6850 at default voltage with all the cards I believe. The higher voltage was only required to get the CPU through post without causing some strange failures.
Therefore I'm not sure if my PSU is limiting the 5830 overclock. It's a 800W quad rail with 20A on each, so I should be good to go but my post experience is telling me it might be limiting. I've been running the 5830 at default since the boot and hanging issues - now I've sorted those I will try and push the card again. Last time out I settled on 865 and 1100, but you may get a lot more.
I'll never know the real cause for certain unless I change my PSU! But this PSU should be good for crossfire. Strange.