I think some people worried that the 930 wouldn't overclock as well as the 920, but the batches of the 930 released so far have shown to have even better OC potential than the 920 (no guarantees, of course). You also get an extra multiplier!
So, for the same price, i would definitely get the 930.
It's debatable. The i7 930 has an extra multiplier, 21 whereas the i7 920 is 20. The i7 920 is a tried and tested cpu, with proper cooling (and knowledge) it will keep up with the i7 975 so why was the i7 930 released. I can't help but think it's been sabotaged slightly by Intel to make the more expensive models more appealling. But I'm only guessing!!! I haven't tried a 930 yet, I've thought about getting one to test but it would take some of my video card upgrade money. I would get the i7 920 and use the few dollars saved towards an even better heatsink.
I say 920. The few 930's I have seen don't clock nearly as well as 920's in the 4-4.2 range. What I mean is, typically a 920 will need less volts at the same clock than a 930. That is only what I've noticed from the couple 930's I've seen though.
If you really want to OC, look around some forums, like Anandtech and [h]ardforum, and try to find someone selling a proven "golden" batch. I've seen great chips that can do 4.5 stable at a mere 1.3v
I have worked with one 930. It clocked better than my C0 and relatively close to what I see from D0 steppings. I would not say it is better but it is real close to the 920. Luck of the draw is always a factor.
The real question is: When are the next cpu technologies coming out? I mean, the i7 was introduced about two years ago, so something must be on the horizon soon, right?
I got a core 2 duo e6600 about a year after its release, waiting for the prices to go down and performance motherboards to be perfected. That ended up costing me huge because the processor, after two years, saw the i7 come out and the i7-920 has been the same price the WHOLE time. I really want to get a i7 system but I feel like later this year or early to mid 2011 something new will be out and make a $1.5K build usable for about a year... I have experimented time and time again to find you can only get one GPU upgrade with a whole system build, then the CPU will bottleneck and force you to buy a whole new setup!!!!