the IC7 uses intel's i875 (canterwood) chipset, while the IS7 uses the i865 (springdale) chipset. orion mentioned that a P4 2.4C and an IS7 would be the best bang for your buck b/c right now the 2.4C is the cheapest 800mhz fsb and hyperthreading intel CPU (AND probably intel's best OCing chip right now as well). the IS7 is not Abit's full-featured mobo. Abit's top of the line i865 board is the IS7-G. if you
here you'll see the differences btw the IS7 and IS7-G, as well as several other boards.
some say that intel's chipsets are "binned" like their CPUs, meaning the best chips become i875's and the ones that come in below it become i865's. now i've never read up on it, but these chipsets are extremely similar, i.e. both have the ability to use intel's new CSA bus, provided the mobo manufatcurer wants to implement it in their design, both use the MCH northbridge, both use the ICH5/ICH5R southbridge. of course this all depends on which version of springdale you're talking about (there are 3 versions of springdale - 865P, 865PE, and 865G, while there is only in canterwood - 875P). now the 865P doesn't officially support DDR400, but the PE and G versions do, making them almost identical to the 875P. i suppose this is all very strong evidence to suggest that the chips are the same, and just binned based on performance.
one other thing intel did to make the chipsets different was to include PAT (performance acceleration technology or something like that...) with the 875, and not the 865. however, certain manufacturers (Abit and ASUS, maybe others but i don't know...) have been able to mimic intel's PAT code, and have implemented it in their 865 boards. example: the IS7, although an 865PE board, has GAT (Abit's version of PAT) w/ certain revisions of the BIOS, 13 and 14 to be specific.
so the facts that there is little difference btw the 875 and 865 and the 865 can be had for much less $, the 865 chipset is the best bang for the buck. however, i see many people buying the IC7 max3 anyways, so if you have the money, why not? i don't have the money, so that is why i'm using the IS7. and when i get a little more, i'll be doing just as orion suggested earlier and getting a 2.4C. but it sounds from your post about going w/ intel's top CPU right now, that money is no object, or at least you don't mind spending the extra $ on your system, in which case i would also get an IC7 max3.