The 5870 is 5/8s of an inch longer than a 260. Bah quote didn't work. I saw dethadder said it looked a smidge smaller. I had to cut reliefs in my hard drive cages when I replaced my GTX260s with my 5870s. (5870 CrossfireX am a suk atm)
In my defense, I was judging by his KB which is very different design than mine 
. Your are correct though. In a review it says it is 11.1 inches long, whilst my BFGTech GTX260 OC2 is 10.5". I think I'd also have to cut into the HD cage to shoehorn it in my tower.
