Conclusion
As far as overall results go, the 8800 Ultra experienced more than double the performance loss with the core clock compared to the other clocks. The GTX260+ however is reasonably even across all three clocks, each showing an average performance drop between 2% and 3%. This is likely because the GTX260+ is a more balanced design than the 8800 Ultra, and also possibly due to the different selection of games being used.
So while it was a given to increase the core as high as possible if you were overclocking the 8800 Ultra, things aren?t as clear-cut with the GTX260+. Some experimentation may be necessary to get optimum performance out of the games you play at the settings you use.