My primary web usage is forums such as this one. Nothing very media centric. My TFF is configured using your preferences file.
My prefs file has an entry in there for web caching. On my system it's caching to a virtual ram disk. The entire app and the browser profile are in ram. But the preference for that directs to my system. If you aren't using that and have not removed it that could be something that is affecting things.
Maybe a quad G5 is acceptable (I've never used one). But it represents the very best PPC PowerMac Apple ever released. The dual 2.3GHz PowerMac G5 I used to own is, IMO, one of the more capable PowerMac system. One of the reasons I decided to get rid of it was it was the web browsing experience was so poor. I couldn't start a long running task, such as ripping DVDs for my iPad, and acceptably browse the web with it while it performed that task. I had to switch to something else to do that. So I figured...why keep it?
It's certainly acceptable in my case.
Don't get me wrong, I'm not there with you so I can't say otherwise or convince you one way or the other. There is compromise involved here, even on a Quad. That said, I have ALWAYS sought out the most powerful systems I could for the price and then upgraded them as far as I could do.
As decent as my tweaks may be, I'm not going to browse the net without purpose on my 17" PowerBook. It's only 1Ghz and has max 2GB ram. There was a time I would, but again, compromise.
The Quad gives me 16GB ram, 8GB of which is being used as that ram disk I mentioned. I routinely leave T4FX up and running and use other apps without an issue.
But not everyone has a Quad, and even less people have 16GB of ram to spare.
That said, what I've done in all my tweaking stems from having to work with a 17" PowerBook with a failed cache and only 2GB ram. So, all in all it's a pretty good job I think. But it's not going to meet everyone's expectations and I acknowledge that. There's only so much tweaking you can do to compensate for hardware that isn't there.
PS. uMatrix or NoScript is a major part of this. If you are not using at least one of those with T4Fx then I can certainly see your issues. Both block javascript, which is one of the major offenders. Both allow you to tune things so that certain JS that you need DOES run.