You should be able to get near the superclocked versions speeds. My 550 ti is @ 951mhz I believe, I would start there and work your way up slowly.
Edit: I thought there werent really any advantages to overclocking anything but high end cards?
There are some advantages, a few fps too.
Too bad the higher binned 550ti's suck at OC, when I overclock above 1ghz from stock of 981mhz performance goes down