The clock speed increase roughly corresponds to the performance increase in GTX480s.
So if it was 5% extra clock, it would be pretty much 5% extra performance, so it depends on how much higher the clocks are. If it's >6% (or ~40MHz) and you don't want to overclock yourself, then it would be worth it in terms of price/performance (also depends on whether it has a different heatsink to stock which might also be good value if you do want to overclock yourself).