Opinions on this budget CPU upgrade please

Hi guys,

I have quite an old PC, and i'm thinking of upgrading my CPU (to a used one), although i'm really low on budget.
I'm using the PC mainly for music production purposes, which involves some real time effects (vst plugiins) which are quite CPU intensive on my current system.
I have an upgrade idea in mind, and wanted to know what do you think about it.

My current system:

mobo: Gigabyte GA-G31M-S2C
CPU: Intel Pentium 4 650
RAM: 4gb DDR2 800mhz

I went through the whole supported CPU list in Gigabyte's website and compared all the best contenders in the budget - which is around 90$.
I found one that was the best of all of them - Intel Core 2 Duo E8400.

Now, i want to know how much do you think this upgrade would be effective, Do you think it's worth it? or nothing below the 130$ range will make a difference?

Thanks