Appears to me that the pricing market is having a fit trying to get all these cards into some kind of equalibium. I seen a decent deal on a 4g version of a card in the 6xx range only £30 more than the 2g version and you got to think to yourself, why would you buy the 2g if that's the case ?
I'm advising to wait until everything settles down. I see the 680 getting the usual post-launch deductions (which I think are coming into effect, only the better stores are applying whilst others aren't, most noteably Aria are showing some great prices - elsewhere the same cards are £50+ more). The 690 will drop in the same fashion, although with these being rare, the stores may still hold out on keeping the prices up - that and they're a niche market. .... then the 670 comes along at a fair price, which itself will drop in around a months time.
Crazy business !!
I envisage, in around 2 months, we might have a situation where 680s don't fill a price bracket that infringes on the 670, same with the 2/4g variants, the full range will then come out and with any luck, supply will be great and not just Aria will be trimming the prices are they're supposed to.
When it's all settled down..... then you got to worry about the 8970 !! lol