It's really a two-fold thing between the 460/470. First off, the 460 has a higher stock clock. To get the same percentage increase from stock, you have to raise your clocks farther than I would on my 470. 10% for me would require +60, whereas you would require +67.5. And because the 470 is faster to begin with, you may be fooled just by the numbers themselves. You have a stock score of 2000 and overclock by 10%, +200. If you have a stock score of 3000 and overclock by 10%, +300. Technically the same jump.. but the scores may be deceiving. And this isn't to imply that a 10% overclock would make for a flat 10% performance increase in every bench(vantage is really all I would trust for this kind of pinpoint accuracy), but you get what I'm trying to explain I hope.
You're obviously trying to squeeze every last inch out of what you got though, so did you happen to notice
this?