I have a system with the following relevant specs:
Mobo: MSI z68a-gd80
DRAM: 2 x4 GB Corsair CMP8GX3M2A1600C9
cooler: Noctua NH-D14
The major activity this box has is folding. This is the first time I've built a machine or overclocked. The MSI board has lots of easy overclock support, and it auto sets voltage, but seems to have limits with this. Generally I find that an overclock to 4.2 mhz is stable, but when I've tried 4.4 and 4.5 it will boot up but the system hangs under load within about 5 to 10 minutes. Since I've seen that the CPU can run stablely at significantly higher ratios than I'm using, I suspect that to go higher I'll need to manually play with voltage. I've run the system for about 4 months now OCed to 4.2 ghz, CPU temperatures are within normal expectations for the NH-D14, and the system is generally stable.
My question comes from some changes I made yesterday that had a strange result. While investigating slower than expected folding times, I realized that I had not set my memory timings for the memory's rated speed; it was running 7-7-7-20 which according to the MSI control center app's timing tables is 533 mhz. I changed the settins to the timings for 800 mhz, which are 9-9-9-24. I made this change in the BIOS, and also enabled XMP mode, which was disabled. I'm pretty sure these were the only changes I made to the memory settings. I also was looking at CPU settings and noticed the hardware virtualization was disabled, and I enabled that as well as soon I'll be running a vm on this box.
I noticed later in the day that even though I had made no changes (so I thought) to the CPU overclock setttings, that the machine was reporting the CPU speed as 4.33 mhz instead of the usual 4.20. The BIOS reported that the BClock was 103.1 mhz with a 42 ratio. When investigating this, I also noticed that the bios allows for changing the bclock. As the machine had been operating for several hours under 100% CPU load, I left it alone. But this morning, I had a blue screen while I was away from the machine and I reset the bclock to 100mhz. I have gotten unexplained Blue screens on rare occasions, but this was the first one in about a month or so and so I suspected that it was related to the changes from the day before.
My question: 1) I thought the 2600k had a locked bclock, and CPU overclocking was only possible by changing the ratio. Does changing the setting actually have any effect with this processor/mobo setup?
2) not a CPU question: I believe the mobo's memory speed is 533 mhz. So does it matter whether I have timing at 7-7-7-20 or 9-9-9-24? The system seems stable in any case.
The bclock is NOT locked, but it has a very limited range of stable changes. When I auto-OC, the ASUS software always sets bclock to 103.1. But that setting does not allow me to get the best overall OC, so I set it back to 100 manually and then crank up the CPU ratio a little more.
For me, memory has always been "set and forget" because I don't believe it affects performance very much. I turn on the XMP profile, which results in 800 MHz (x2 = 1600 MHz) and 8-8-8-24 (I think...). You should be able to use the same settings with the RAM you have.
You didn't mention the vcore setting you are using - you might have to raise it a little to get to 4.5GHz. From what I've seen, 4.5GHz is generally achievable for the 2600k.