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 With the new 400 series dropping in about a month, why purchase a soon to be outdated card unless you get a good deal ?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