I want a new dual (maybe more?) head card.

Is it possible to have the second monitor performance as good as the first??
IE: OpenGL..

Ive been fooling around with dualhead/xinerama with a agp card w/ an old pci card.
The performance is not so good. I cant get opengl to work on secondary monitor.
I can play movies on the secondary monitor if I dont use the xinerama exstensions.
If I use xinerama I cant play a movie on the secondary...and no gl!!
However with xinerama extensions everything still works on the primary.

My question...

What do I have to do in order to have two monitors the way I want??
Which are the best graphics cards for this?