I have been using that exact card with 2 22" monitors for several months now. It works great. I saw that it might be overkill. It may be, but I've tried to eliminate any latencies. Whether or not it is overkill depends on the amount of data that is being converted into video data. I have many charts with indicators and a scanner. I am doubling my monitors to 4 this weekend.
Bought this card for about what your looking to use it for have it on 2-22" monitors and it has worked flawlessly. Picked it up for $90 from newegg and dropped it in myself after watching a youtube video on how to...very easy to do... XFX PVT84JUDF3 GeForce 8600 GT 256MB 128-bit GDDR3 PCI Express x16 SLI Supported Video Card
http://www.youtube.com/watch?v=a6Oo79f742Q&feature=related That was yesterdays trades, look forward to monday http://www.youtube.com/watch?v=DNt0RmK5Ewk&feature=related