That's a lot of if and buts and a fair bit imagination![]()
One can but hope. And dream

Do we know that?Really we can't be sure as to how well the GPU cores will fare. What we do know is that the GCN cores in Kaveri are far less memory bandwidth sensitive than the old VLIW4 cores.
That Tom's Hardware link I referenced above seems to show the 7730 (GCN) acting very much like the 6670 (admittedly VLIW5, rather than the VLIW4 you refer to) in terms of GDDR3 vs DDR3
No, I was probably getting carried away. At stock clocks, it would likely match Sandy per core. But that's because Sandy is clocked lower. IPC would still be behind, as you say.Needs more than 15-20 to match Sandy (Except in those exceptions where SB's instruction sets are lacking)
Even then, 15-20% is still a decent gain with a half decent IGP.
An 8 core with 15-20% over PD will still be very impressive though.
But it's not Sandy IPC.