I strongly doubt there would be a noticeable difference between the two. Even when using the computer to its fullest potential, it wouldn’t be the processor holding it back from going further, it would probably be the memory (since. its slow, in comparison to the bus speed of the processor). In essence, even though you would have .3 more ghz’s processing power, your computer wouldn’t be able to “think it” quite so quickly, because of that delay.
Also, because the hard drive on the macbook is 5400 as previously stated, the computer wouldn’t be able to do anything with that data as quickly as it was thought out either.
To summarize: 2.4 would be, in practice, overkill.