Well, the difference between an octo-2.8 and a 3.2 will be enormous, and the difference between the 3.0 and the 3.2 will be huge.
And by enormous, I mean unless you're benchmarking and record the times taken by the 2.8 and the 3.2, you'll never notice the difference- to the point where someone might be able to convince you in a blind test that the 2.8 is faster with power of suggestion.
By huge I mean you'd have to peer pretty closely at the screen to see any difference in the numbers the two put up. I mean, come on. Do the math. 3.0 to 3.2? That's what? 6.6%?
Think about it this way... It's ten years ago, and you're buying between a 280, 300, and 320 MHz G3 (pretending they were running a bus speed of... I guess 80 MHz), and they all have the same cache size. Which is fastest? Not really a huge difference... particularly once you clocked your 280 to 340 MHz.
Fact is, you'll never notice the difference..