This is what I am thinking...supposingly the GTX560Ti 448 1.3GB is launch at 6950 2GB/GTX560Ti 2GB's price point (around £200), it is not unlikely that there are manufacturer releasing a GTX560Ti 2.5GB for around £230~£250. With just 32 fewer cores than the GTX570, I seriously doubt it will be slower than the GTX570 by much at all...so that would probably be the card with the best of both world in terms of GPU grunt and VRAM IMO.
But like I said many times before, it's best wait for next gen cards that are on 28nm, and see what happens.
A 488 with more ram might be interesting, but if this card really is limited edition it's a bit unlikely.