I used a Matrox G550 AGP dual head together with a Matrox G450 PCI dual head (so quad-screen) setup for years without problems. Matrox drivers are great in such an environment.
Got multiple quad cards, waiting in the wings. Used matrox quad cards are cheaper than 2 new dual. If 1 dual card goes out, just put in the quad card. Beats being dropped down to 2 monitors. Another great set-up, idea: If you MUST have some 128+mb cards....like gnome said go real deal ATI duals.Get a cheap matrox quad to put away for back-up, if one of the duals goes out. It's a great cheap back-up, and allows you time to get another replacement dual.
Thanks for all the advice. I installed a second Radeon card on my Dell 4700 and now I have quad monitors. Jeff
I have had 1 matrox G450 and one G550 for 2 yrs now, running quad monitors. I've been thoroughly impressed and have not had any problems. I just recently bought another matrox for PCI, to have 6 monitor capability. The reason I didn't get 4-in-1 is for the very reason of redundancy.. I can deal with the loss of 1 card, and work for a couple days with only 2 (now 4) until CDW shipped me a replacement. good luck on the new setup