Xeon quad-core 2.66 for photo and video editing?

Hi everybody!

First of all I apologize if similar thread exist. I searched but didn't find.

I have iMac24" Core2Duo 2.8GHz with 4GB RAM, Mountain Lion and latest Aperture which I use for editing Canon 5d mk2 RAW files and it is sooo slow! Some times when I use dodge brush and use it on highlights only I have to wait 10-15 seconds just to see the result of brush stroke etc. When I use Aperture I have to close all other programs to make is usable which is also annoying. It is slightly faster when I use Lightroom but I don't like Lightroom.

I have opportunity to buy used Mac pro Xeon quad-core 2.66 GHz, 8GB RAM for fair price so I was wondering how much faster is that computer from the one I own now? Would I notice a big difference or is it not worth spending money on that one?

I would like to do some video editing too in future.