The difference is an increase of 25mhz in boost clocks on the OC version, which is nothing those two cards would perfom pretty much identically. The cheaper card could very easily be manually overclocked to the speeds of the OC version and beyond, so I would say there is no point at all in getting the OC version and I would personally get the cheaper one.
Both WindForce 2, except the OC model is overclocked a tiny bit from the factory and normally nothing to stop you hitting the same overclock on the standard card.
The difference is an increase of 25mhz in boost clocks on the OC version, which is nothing those two cards would perfom pretty much identically. The cheaper card could very easily be manually overclocked to the speeds of the OC version and beyond, so I would say there is no point at all in getting the OC version and I would personally get the cheaper one.