It will fit! No problem!
Go to the Storm Scout website and see what size cards Cooler Master actually states it can take. Then go to the 5850 site and see how long it is.
You should be able to work out for yourself then if it fits.
No offense dude but this is simple research that you can do yourself, you don't need us to do it for you.
I did go on the website and I found the dimensions. There were no internal dimensions let alone dimensions for the expansion slot area.