It doesn't mean a thing. Asus have a different fan control profile to other brands, but there's nothing wrong with the normal one, because I use it. There's no need to stay away from Asus as a graphics card brand, but for the 4870X2 at least, there's nothing that makes them any different to any other brand, so if you can find a cheaper card by someone like VisionTek, go for it. Try and find a manufacturer that provides a warranty though, as Powercolor do not.
Unless you use a 30" monitor, it can play ANYTHING maxed out, and I mean anything, Crysis included, so I'm very doubtful Dead Space will prove an issue.