PowerMac D 1.8 to D 2.5 ???

I currently have a G5 Dual 1.8 with 2 GB Ram and 450 GB of HD.
It is used strictly in my studio for music production.
I've been a PC user my whole life and recently switched about 6 months ago and now I am a true MAC ADDICT!!
I was wondering if anybody has made the switch from the D 1.8 to the dual 2.5?
Is there a noticeable difference in speed? I have asked Apple and of course they say yes but I wanted to hear it first hand from someone not just trying to sell me one. I will spend the money because I am a speed freak and always want the best for me and my clients so any information will be great.
I might just end up filling the memory to 4 GB and keeping my D 1.8? Any suggestions?

Also, can anyone give any good tips on how to keep my G5 running smooth and fast?
Thank You
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I havent switched from one to the4 other, but have used both extensively. the biggest difference will be when running processor intensive apps, or many at one time. the front side bus speed also has A LOT to do with it.
as far as keeping te g5 running smooth, repair permissions after installing any software or hardware, and after updates, and whenever a problem arises. repair permissions at least once a month. if you can, use an app like cocktail to run cron scripts. also reset the pram after a problem occurs and repairing permissions doesnt fix it. for major problems, use fsck.