From the Geekbench benchmarks they look about on par with the higher clocked models, at least as far as you'd notice. I guess the difference might come under sustained load, but they seem pretty decent.
It's the MacBook Air that is underpowered. The new Pros are fine, but Apple does need to stop shipping them with a puny 128 GB SSD and go to 256 GB as standard. SSD prices have come down and there is no longer any excuse for the 128 GB SSD.
Exactly. Geekbench doesn’t measure sustained performance. Burst-wise, all these CPUs will be within 10% of each other anyway. In more sustained test I expect the new quad-core to be 30% faster than the old dual-core.