the backplate should not be a problem, never experienced a card not fitting just because of that.
the backplate adds a total of about 2mm of hight to the card at max.
it sits on some of the components on the back side of the card using thermal pads and is made of 1-1,5mm thick aluminum.
the total hight of the card is 111.15mm, including the backplate.
 
so all in all I think clearance should not be an issue at all. 

Thanks for the replies! 2mm.....I think that will be ok, but going to measure the space between the 580 and memory lock tabs anyways before I spend that much money. Thanks again sahafiec!
 
Yeah Vlada011, I'm over due for a upgrade, and thinking about 4k in the near future. 

Well I finally let go of the cash and ordered a 980ti ftw from Amazon.  Wish me luck that I get a good card! 
 
I remember this feeling from 45 years ago, when I was young, and it was a day or 2 before Christmas. 

Got my 980ti ftw today and wow what a card it is! Fit in the case just fine. Unbelievable upgrade from 580.
GPU clock boosts to 1380 in stock configuration while playing World of tanks with DSR in 4k mode , while running at 52C. I am well pleased to say the least. Now I  need a better monitor.
 

I don't do much benching but i did run a 3Dmark performance for some comparison of the 580 vs 980ti ftw.