The superclocked ones are '"hand picked" and guaranteed to run at that speed. Very often however, you can manually OC the "vanilla" version to the same speeds but it's not "automatic". Most times you can, sometimes you can't.
I'm surprised you can find a 275 either way. With the new 400 series dropping in about a month, why purchase a soon to be outdated card unless you get a good deal ? From what i have seen last month, nVidia cards are selling for 25-30 % more than they were 3 months ago....and I can't call that a good deal.
The most expensive Nvidia 200 series card I could recommend at this point is the XFX 250 GTS 512 MB at $99
GTS250 is NOT a 200 card. Its a G92 9800GTX. Is a good card if you can find one for $100. Last I saw they go for around $130. I agree with the others. If you have the $270ish for the GTS275, get the 5850.
Yeah If you have your heart set on a 275 get the vanilla since 99% of the time you can easily hit the OC versions speed with riva tuner or evga precision.
However, a 260gtx can easily OC to be just as fast a 275 and if you get lucky almost a 280. I had one a little while back that hit 730 on the core. It was just a tade bit slower than a 280 and it was only $180. With a voltage mod bios you might be able to get even higher.
I now own a 5850...I loved Nvidia but between the crappy high end cards they are selling now and the lack of Fermi I am afraid our love is official over...for now