I own both an EVGA 8800GT SSC and an EVGA 8800GTS 512, and I can say from personal experience: Get the GTS!!!
The fan on the GT is just f@cking annoying! When it spins up, it makes this incredibly loud high-pitched whine that I can hear even while playing a game with the volume cranked up. Despite the noise, it barely keeps the GPU cool enough, and in certain games, I get artifacts, lock-ups, and even crashes, and all this without ever having overclocked the card.
The GTS on the other hand comes with a much better cooler and bigger fan, and is barely audible even at full speed. Even when overclocked, it has yet to produce the same stability problems the GT had.
Bottom line: the GTS draws a tiny bit more power, but is faster, more stable, and runs MUCH quieter and cooler than the GT.