One thing a lot of people don't realise about PPC Mac browsers is that the internet is not the same beast it was back when Apple still used PPC processors (for a start, there's a LOT more data being downloaded), so people who make PPC Mac browsers have had to cut features often found in modern browsers. So, pages will load slower than they would in, say, the latest version of Safari on a M1 MacBook Pro.
That being said, the latest version of InterWebPPC works quite well on my iBook G4, which has half the RAM of your iMac, compared to vanilla TenFourFox & especially Safari 4.1.3. Pages that don't load in Safari load in TFF & somewhat faster in IWPPC.
If you're finding that the slowness is bothering you too much, look into downgrading your iMac's operating system, and/or acquiring more RAM for it. Honestly, more RAM is an easier & better fix than an OS downgrade, but an OS downgrade doesn't cost money.