The main reason that i hear people put their pc's in sli is if they have large screens. I have a 17" Princeton... don’t laugh but i was wondering the other benefits of having SLI. I know the frame rates will go up but is it really needed?
No, it's not. Not for you. Not for most people, in fact. You don't need SLI with that card and monitor, the card is already better than the monitor needs.
SLI is needed when you play a demanding game (Oblivion, etc.) on a huge monitor at a huge resolution (1920x1200 or better) and you really want the best settings and your high-end card can't get a decent frame rate. Not your case, is it?
BTW, SLI does not double the performance. The frame rates will go up but nowhere near 100%. It can even make no difference. It depends on game and resolution, even on the CPU. Plenty of benchmarks on the Web, Google them.