Looks like a a good bet of new imacs around April maybe:
http://www.hardmac.com/news/2012/01/30/ivy-bridge-desktop-cpus-updated-list-and-earlier-availability
Given AMD still hasn't fully released their desktop 28nm "Southern Islands" ( 77xx , 78xx , 79xx ) line up, it would not be surprising if mobile 28nm 7730M , 7750M, 7950M to arrive late in April or early May rather than when the Ivy bridge desktop chips arrive. All the more so, if Intel isn't dropping the mobile Ivy's until May/June ( i.e., there is lower demand for PCI-e v3.0 mobile offerings till then. )
As for being "behind" the Core i7 Ivy's. Not much if any. In the line up above the top end is the
i7-3770K: 4 cores, 8 threads, 8 MB of cache, TDP of 77W, 3500 MHz with Turbo mode:3900 MHz,
Whereas the Xeon 1620 comes in at
Xeon E5-1620 4 8 3.6 GHz 10 MB 130 Watt
The Xeon has an extra 50W of power , 100MHz higher base, 2MB more cache, and 2 more memory controllers to throw at the "tick behind" problem. The i7 will certainly have better integrated graphics.
I'd guess that Apple with go with the 3700 which is a 200MHz gap and only in the "deluxe" build to order model.