Video cards, what slots do you put extras in?

I have a motherboard with 2 x16 PCI Express connectors, but one of them is only x4 electrically. I have an 8800GT (G92 512mb) in the main slot, and my old 8800GTS 320mb in the secondary slot. I seem to be getting good performance, with the x4 slot noticeably slower, even at lower resolutions. For the most part I get 35 FPS+ on all the alts and 70-100FPS on the main at 1920*1080 with all the eye candy turned on. I currently run 4 monitors, so I have a dedicated monitor for each toon, except 2 are sharing one. My monitors are older non-widescreen so the 2 sharing a window are rather small, with lots of info on the sides which I don't really need.

My question. I want to add another video card, but I have no more x16 slots, so that rules out powerful cards. I saw a couple PCIe x1 cards out there, which should perform better than a PCI Vanilla slot, but do I really need it? I am 5 boxing with one computer, a quad q6600 overclocked to 3.3ghz, 8gb ram, raptor hdd, 2 8800 video cards, so it's a pretty high end system.

Am I better off buying a third video card to run an additional monitor? Or should I look into bigger widescreen monitors for my toons to share? Or should I look into a motherboard with 3 PCIe x16 slots and get another 8800GT (or better)?

It looks kinda like the command center of the Nebudhadnezzar from The Matrix with 4 monitors just sitting randomly on my desk (its pretty large, so it holds em all) I should really take a pic of it. Especially with the matrix screensaver running. If only I could get different bits of matrix code on each monitor. I guess I could just run looping videos on each, but that sounds like too much work...