ht4u.net made a pretty awesome comparison.
They took a HD 5770 and a new HD 7770. Both cards have 40 TMUs, 16 ROPs with a 128bit SI and GDDR5.
And both have 10 shader-cluster.
The only difference is, that while the HD 5770 has 160 5D shaders, the HD 7770 uses 640 1D GCN shaders.
Now they clocked the HD 7770 down to the same clocks as the HD 5770 and compared the GPUs.
HD 5770: 1360 GFLOP/s, 34,0 GTex/s, 13,6 GPix/s, 76,8 GB/s
HD 7770: 1088 GFLOP/s, 34,0 GTex/s, 13,6 GPix/s, 76,8 GB/s
You can see that the HD 7770 has about 25% less FLOPs, the rest of the cards are almost identical (and keep in mind that the HD 7770 has the better AF).
The results are great: The HD 7700 is up to 37% faster in some games while losing to the HD 5770 only in two games, Dirt 3 & DA2. And there it's a maximum 1.8% slower.
+ drivers for the VLIW5 arch are matured, GCN is quiet new yet, we'll see some improvements here for sure.
So, despite having about 25% less raw power, the HD 7770 is faster in most games, sometimes even by far. This seems like the step AMD needed for a long time.
(This isn't supposed to be about the price of the HD 7770)