CPU upgrade from 2.0ghz to 2.4ghz - Noticable difference?

Some details can be more important than CPU speed - I remember the 4400+ and 4800+ having some other advantage over the rest in the series, but in the bazillion years that have passed since that was hot stuff I've lost that detail. For what it's worth I still use a 4400+ in a roughly five-year-old board (admittedly with faster RAM) and seem to survive well enough.

Jeff
 
just bought an i7 computer for not so much. A session that was 90% Cpu on a dualcore dropped to... 10%. Dramatic improvement.

So don't look back. Dualcore for that low is a big improvement, and when you have a little cash, don't buy new gear but buy a new computer, even not a big expensive one. The difference is so dramatic it will improve not only your convenience, but your "artistic" work on songs. It's so easier to think only in artistic way when you have no need to think of how many % this effect or this vsti takes.

And when your reaper sessions opens in a few seconds and closes as fast as your finger hits the left clic, it's awesome. cause you can say "oh wait i forgot to change that settings", you open your daw, a few seconds later it's done, a few more and your computer is turned off.

it's worth it, really.