I'd be willing to bet that there's some difficulty fetching enough registers to go wider within the cluster. If you want to tweak something in there, you add more texture addressing units, or decrease the issue width to a quad. If the R600 really winds up being good at either modifying issue width or TLP, then the G80 arch is going to need some revisiting for gpgpu competitiveness.
I'm not really expecting any of that in G81, though. If I wanted to "get crazy", I'd go with just a straightforward scaling. 384->512 and 900->1200 would imply (assuming bw:computation balance doesn't change) 10ish clusters at 750/1800. Of course, the chip wouldn't be any smaller at 80nm than g80 at 90nm if they did that, and I doubt it would run cooler either! Unless G80 has a couple of clusters in there for yield purposes that they can unlock in 80nm, I don't think I would expect even that.
Of course, another possible rabbit is 65nm. Hmm, nah. Kirk hasn't been out vigorously denying 65nm.... ;-)
I'm not really expecting any of that in G81, though. If I wanted to "get crazy", I'd go with just a straightforward scaling. 384->512 and 900->1200 would imply (assuming bw:computation balance doesn't change) 10ish clusters at 750/1800. Of course, the chip wouldn't be any smaller at 80nm than g80 at 90nm if they did that, and I doubt it would run cooler either! Unless G80 has a couple of clusters in there for yield purposes that they can unlock in 80nm, I don't think I would expect even that.
Of course, another possible rabbit is 65nm. Hmm, nah. Kirk hasn't been out vigorously denying 65nm.... ;-)