I received feedback in my support ticket to XFX asking about the HD 5850 models. Besides the fact that the non-reference HD 5850s (HD-585X) don't have voltage control, they're larger than the reference HD 5850s (HD-585A). The HD-585X models are 10 inches while the HD-585A models are 9.5 inches. If you have a case with good cooling, any one of them will do but if you're worried about having too much heat inside your computer case or not enough space, I would go with the reference model which vents heat outside of the case. (I am also in a similar situation as you are except my top choice would still be the reference model).