GTX 260 SLI Question.

So I have an EVGA GTX 260 core 216 stock clocked card 65 nm processor and I want to get another one and run it sli.

1.Do I have to get the 65 nm or could I get the 55 nm version?

2.Can I get it from a different vender, like BFG or do I have to get an EVGA brand?

3.Since I have the 216 core version, does the next one I get also have to have 216 processing cores or can I get a 192 version?

Thanks all

-xthekidx

Do the cards need to have the same clock speeds as well? Should I buy a stock clocked card since the one I have is or could I possibly get an overclocked card?