How much benefit do I get going to 5 GB for Logic 7.2.3?

Question

OK, here's the deal...
I've recently come into a little extra cash and I'm considering purchasing a RAM upgrade for my 2.66 Mac Pro.
I run Logic 7.2.3 and I currently have 3 GB RAM and a separate internal 300GB drive for audio.
In Logic, my songs typically use 15-25 tracks or so comprised of audio files and loops, virtual instruments such as Kontakt 2.2, Guitar Rig 2, Dimension Pro and Stylus RMX. My songs usually have Ableton Live 6 and Reason 3.0.5 rewired as well. I sprinkle a few Space Designers into the songs here and there.
That said, here is my question:
Considering how Logic and OS X handle memory, how much benefit would I really see if upgraded to 5GB versus just upgrading to 4GB? Am I correct in assuming that I'd need to wait until Leopard to see benefits beyond 4 GB?
I only ask because Mac Pro RAM modules are kind of expensive and I don't want to overpay if its not needed. I am hoping that some of you Logic experts can help me out on this!
Thanks,
Ken
Mac Pro "JUGGERNAUT": 2.66 GHz, 3 GB RAM   Mac OS X (10.4.8)   Logic Pro 7.2.3 User

Answer 1

On PPC machines, I used to have 4GB and went to 8GB as I cannibalized another machine, and I was surprised that memory above 4GB did seem to make a difference. I do run external programs quite often, like Melodyne Studio, so I assumed that it would help a bit, but I found that on bigger song files I think I noticed increased smoothness and stability.
So perhaps Logic + OS does benefit from increased RAM more than conventional wisdom has suggested. Particularly as you're using processor intensive plugs. I don't know if using these instruments can benefit from RAM over and above Logic's partition in Intel's architecture.