I was correct based on the chart... 30% isn't correct in any way. (Or is it...?)
To be thorough we should be using the 1680x1050 chart rather than the overall performance chart posted above.
The Lightning Edition GTX 460 has a factory OC of 12.8% over reference on the core. Assuming(probably incorrectly) that performance scales perfectly with core speed and (probably correctly) that the doubled memory doesn't give much if any benefit at that resolution that would put the OPs card at 77% on the above chart. Ironically the OCed GTX 460 is then almost exactly 30% faster based on that number.