EVGA ahs some great perks. models ending with AR have a lifetime warranty and the option of upgrading using EVGA's step up program. Models ending with KR have a 3 year warranty and the option to buy an extended warranty from EVGA which then also gives you the option of upgrading with the step up program.
If the model numbers of two cards are the same except for the last two characters (AR vs KR) they are identical cards and only differ in their warranties.
For example, look at the following two cards:
EVGA 01G-P3-1561-AR: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=7191450&CatId=3669
EVGA 01G-P3-1561-KR: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2148471&CatId=3669
They are both same price so grab the AR one.. lol you would be stupid to grab the KR one. They aren't always the same price. The AR one is usually somewhere between $5 - $75 more than the KR one.http://www.evga.com/support/warranty/http://www.evga.com/support/stepup/