Confusing? I'd say!
Even though the model name is always shown as GA-P55-US3L, the actual chipset can vary:-
Board Revn. 1.1 = P55
Board Revn. 2.0 = H55
Board Revn. 2.3 = H55
And they're all ostensibly full ATX. However, that's not altogether the case. The above three measure a little less narrower than full ATX (but not mini or micro ATX). See my recent posting on the matter of the board's physical size. However, most case mounting plates will have standoff positions for that size. Mine does.
Quite a number of UK retailers are still selling Revn. 1.1. As for 2.3, I've yet to find any UK retailer that has them. I don't think 2.3s have been shipped to the UK yet, and may not be for quite some time - probably not until all stocks of 2.0 in the UK have been sold.
As someone who's been wanting to buy Revn. 2.0 of this GA-P55-US3L board for some weeks now, I'm having a really difficult task in locating one that's at least Revn. 2.0 and which will come guaranteed with the manufacturer's seal on the box intact. I've contacted several UK retailers on those two counts and all I'm getting in response from them is complete silence.
I don't think that second lot of links you've given, DM, points to any boards that are anything to do with the GA-P55-US3L. They're completely different boards. However, they do serve to illustrate the constant changing around of P55 and H55 chipsets on these families of boards. It pays to look at the specs very carefully indeed and to research the advantages and disadvantages of the respective chipsets.
It hasn't helped that Intel has also been revising manufacture of some of its i5 and i7 Skt 1156 CPUs (changed stepping).
