Hi there,
 
I own an EVGA GTX 780 SC ACX 3GB, part number -03G-P4-2784-KR- with bios version 80.80.45.00.80 (P2083-0021). Got it brand new!
 
I'm thinking of getting another one with the exact same description from a friend of mine, but different part number -03G-P4-2782-KR- and probably different bios.
 
They are exacly identical, box is the same, both SC ACX but the part number (and probably BIOS) are the only difference.
 
In order to SLI these two, the questions are:
 
1) Is it possible, or the part numbers must exactly match?
2) I know that the bios can be flashed, but i'm wondering if they must also match.
 
Thanks in advance
Cheers

Thanks for the fast answer,
 
Ok, they're exactly the same.
 
Another question: the clock speeds, core and voltage and all that stuff must be exactly the same in both cards or "SLI system" ignores the clock speeds of the second card some how?
 
 
 

The GPU's need to be exactly the same for SLI to work.  So you need the exact model number.  I asked the same question of customer service and that is what I was told.  I wanted to add a third 06G-p4-2795-Kr to the two I had the 3 way SLI and they said they had to be the same GPU or it would not work.  I can't find a third 2795.  Not available.
 

rmbenian
The GPU's need to be exactly the same for SLI to work.  So you need the exact model number.  I asked the same question of customer service and that is what I was told.  I wanted to add a third 06G-p4-2795-Kr to the two I had the 3 way SLI and they said they had to be the same GPU or it would not work.  I can't find a third 2795.  Not available.

Well, you listed the same model number twice there... The model numbers do not need to match exactly and evga techs have stated this on these forums. 
 
And yea forgot to mention the clockspeed deal, they will default to the slower card. They can however run different voltages without problem. You can still overclock in sli as well but your limited to what the slowest card can do. 

Careful on SLI'ing the GTX 780i's, some (or all, or just the 6GB models, don't know which) of them are weird..EVGATech_ChrisB confirms that they need to have the same Device ID as well or it's a no-go..See post #36 here..There's a fix/workaround though that Sajin posted in post #35 should you need/want it..If SLI don't work and the Device ID's are different, that's prolly why..Just a heads-up.