I have a EVGA GTX 550 Ti 02G-P3-1559-RX card. My friend has a
EVGA GTX 550 Ti 02G-P3-1559-KR that he used for a couple of
months. To him bigger, faster and more expensive is better especially
if you have two or three of them so he's upgrading and wants to sell the
550 to me at a good used price. My question is, can I use this card with the
550 that I already have SLI? I checked the specs on both cards and they are
identical except for one has RX on the end and one has KR on the end and my
card has 2000MB GDDR5 memory and his has 2048MB GDDR5 memory. Any help
on this will be greatly appreciated and will determine if I buy his card or not.

yes you can, as long as it is a gtx 550 of any kind (550, 550ti, 550 sc) It is important that you buy the same card with the same memory so that you are not having a card depending more on the other. 

I use to have a gtx 550ti SC, with 2gb of ram, i noticed that i could not play skyrim on maxed out graphics including a few mods that would only run at 30 fps.  Now that i have bought a 2nd gtx 550ti 2gb (this one is not superclocked) i am now able to play with everything on max, and some new texture mods i downloaded even at 60 or higher fps.  FYI, you can always adjust the clocks on the card by using precision x.  This will make the card work harder on the otherhand.  But since i did not buy the sc edition, i simply just overclocked my new card to match my sucperclocked card.

sorry for thread jacking guys. BUT, can these cards do TRI SLI??

i bought one yesterday and wanted to do it fo fun and giggles and do nto want to buy 3 if it can only do sli.

cheers
levon

this may be a dumb question... i'm wondering if its possible to sli a evga 550 ti and a asus 550 ti.. im kinda new at all this but i wanted to make sure before i did anything dumb lol thanks for any feedback!