Upgrade: Monitor or Video Card?

Hi,

Relevant specs:

CPU: Core2 Duo E6750 @ 2.66Ghz
RAM: 2 x 2GB
Video Card: nVidia 8800GT OC
Monitor: Dell 1907FP (1280 x 1024)

I have a $300 budget on upgrading this box, and I'm thinking either the monitor (been wanting more screen real estate, like 1920x1080 or 1680 x 1050) or the video card. I'm not sure which based on the following:

1) Upgrading the monitor: If I upgrade my monitor to a higher res, I risk a decrease in FPS making some game unplayable.

2) Upgrading the video card: How much of a performance increase will I see? Borderlands runs at a fairly good clip, CoD4 (and hopefully MW2) runs at 60+fps. I can't think of any games coming in the near future that my 8800GT OC can't run at ~60fps. Most of them are designed multiplatform and thus must run on the 360.

3) I've considered buying a monitor for ~$200, and running another 8800GT OC in SLI. Thing is, I can't find any place that sells these cards anymore.

Anyone have any ideas or suggestions? Thanks in advance.