ogl and compositing are two different things. Although compiz et al use ogl for displaying the composited result, there's a lot more to compositing than that.
IIRC it should be possible to combine both, but there are some X bugs leading to trouble. Those could be fixed with time and efford, but nobody has done so yet.
Ouch, that sentence structure looks awful and can't edit. Anyway, I don't know if shatter exists yet and if it does, it probably doesn't exist in old enough X to support fglrx. Whether or not fglrx requires it to work properly, I don't also know.
how dose xcinerama help? In xcierama triple head mode ogl still has to create a 5040x1050 surface. or not? just like in xrandr?
Super annoying edit policy:
And kwin composing also creates a 5040*1050 ogl surface, witch works fine.