There is tremendous amount of SKUs available for the GTX 260, but if you are in the U.S you only should concern yourself with those that end with AR or A1. The rest are for different regions. The two A versions denote the same card, but the A1 versions come bundled with a game.

Beyond that, the next biggest concern is the fabrication process. The GTX 260 comes as a 65nm (nanometer) process or a 55nm process. As technology advances, the nm size shrinks. The smaller fabrication processes runs much cooler and are more power efficient than older processes. The first GTX 260 series and also early 216 core versions all came as 65nm. Users debate the overclocking potential between 65nm and 55nm, but that is beyond the scope of this discussion.

Also of note is ‘Core 216’ found in newer cards. Early cards had 192 cores. The nomenclature varies, but you will hear the word ‘cores’, ‘CUDA cores’, ‘processors’, or ‘stream processors.’ These all mean the same thing. The improved 216 core line was released in response to the popular Radeon 4870. It outperformed the Radeon and was also compatible with a 192 core version in SLI mode. If you are interested in water cooling, EVGA released the “Hydro Copper” version in 192 and 216 cores. Both of these water cooling solutions were manufactured as 65nm.

The final set of differences between these cards is simply the clock frequencies and onboard memory. The following table contains that relevant data for the entire AR line of GTX 260 cards produced by EVGA. There is also trace evidence of a 1251 version of the card, but no other details seem to be available. I prepared this table by hand using cross-checked data from various websites, press releases, and spec sheets.
Please do not reproduce it without permission.

Model Core Memory Shader Size
896-P3-1255-AR GTX 260 Core 216 576 1998 1242 55nm
896-P3-1257-AR GTX 260 Core 216 SC 626 2106 1242 55nm
896-P3-1258-AR GTX 260 Core 216 SSC 675 2304 1458 55nm
017-P3-1165-AR GTX 260 1792MB Core 216 576 1998 1242 55nm
017-P3-1166-AR GTX 260 SC 1792MB Core 216 626 2106 1242 55nm
017-P3-1167-AR GTX 260 SSC 1792MB Core 216 675 2050 1458 55nm
           
896-P3-1260-AR GTX 260 576 1998 1242 65nm
896-P3-1262-AR GTX 260 SC 602 2052 1296 65nm
896-P3-1264-AR GTX 260 SSC 626 2106 1242 65nm
896-P3-1265-AR GTX 260 Core 216 576 1998 1242 65nm
896-P3-1266-AR GTX 260 FTW 666 2214 1404 65nm
896-P3-1267-AR GTX 260 Core 216 SC 626 2106 1242 65nm
896-P3-1268-AR GTX 260 Core 216 FTW 670 2304 1404 65nm
896-P3-1269-AR GTX 260 HC16 684 2214 1404 65nm
896-P3-1270-AR GTX 260 Core 216 HC16 648 2106 1404 65nm