Quad Core vs. Duo Core

Hi guys.

I dont usually post on here often but I'm looking for a little advice now as I need to update my Mac.

I'm currently working with a late 2009 iMac (Upgraded RAM) running Logic 9. I mainly produce electronic music and when I get to the 40/50 channel mark I start getting the dreaded system overload! It then become a matter of bouncing stuff down or freezing tracks which is a pain in the arse!

Anyway, I'm looking to upgrade to one of the newer iMacs that feature quad core processors but I was wondering how much of an improvement I'll see? Has anyone else made a similar upgrade?

I know ideally I should probably upgrade to a tower Mac but my funds wont stretch that far!

Here are my current iMac specs

The iMac "Core 2 Duo" 3.06 21.5-Inch Aluminum (Late 2009) features a 3.06 GHz Intel "Core 2 Duo" processor (E7600), with two independent processor "cores" on a single silicon chip, a 3 MB shared level 2 cache, a 1066 MHz system bus, 4 GB of RAM (1066 MHz PC3-8500 DDR3 SDRAM), a 500 GB or 1 TB (7200 RPM) hard drive

And a link to what I'm thinking about getting....

Configure - Apple Store (UK)

Any help or advice would be great!

Thanks in advance