As Josh says, Core all the way. A vRam clock speed increase can improve certain very specific scenarios, say for example one of Vantages "features" tests might be 2% better with a 50mhz vRam boost. But in REAL terms it's core all the way in my experience. So much so, I haven't bothered to overclock vRam since my old BFG 6800 graphics card
Really? I've OC'd the ram on my 570's and it made no difference in-game, I did the same for my older GTX 275, again no difference. We also did the same with my friends 480's - no difference. This is why, while I DO have profiles with the Core overclocked, I don't for the vram.
Possibly certain titles benefit, the ones I'm playing do not however.
Also, a 100mhz vRam OC on a 384bit memory bus (like wot my 570's are) is going to be worth 50% more bandwidth than the same on a 256bit bus... in theory. Real world doesn't realise this though, but specific bench marks can give you that feel good factor from a vRam OC.
As an aside, when I've played with system Ram overclocking in the past, I've noticed certain benchmarks LOVING it. I.e. 5% on ram = 5% boost in certain (very specific) bench marks. Given that some of these benchmarks are in-game ones, you'd expect maybe something during gameplay but I've not seen it myself. Again, I play limited titles so possibly some thrive on it.
@Drakkonen: Ok, you've sold me, that 2fps is SOOO worth it
It was 1920x1200, which sometimes manages to use up about 1.8GB of VRAM according to afterburner, so I was expecting a little more out of the memory overclock than what I got. My only point was that it doesn't (In my experience) seem to make any more difference than it did with the previous generation in real world tests.