GPU question

[anthanator2]

i'm not the most knowledgeable on PC parts at the minute (learning as i go before doing my first build) but when looking at potential builds i keep noticing there is so many different versions of the same GPU (such as multiple different GTX 1080's )

what is the difference between all the different models of the graphics card and is there any pitfalls when picking between them?

 

[anthanator2]

Another quick one, what is SLI?
I understand that it allows multiple GPU's but that is as far as my knowledge goes. Is this a form of future proofing to allow more graphics capability in the future? Or is it something that would be needed now for certain things?