The problems you are having in the Bronze Doors Region are due largely to the Waterfall that thunders down the ravine underneath the Fortress.
1. Use Software Update to get Mac OS X Version 10.3.9
2. Go to the link to this post I made in another thread:
http://hydlaa.com/smf/index.php?topic=26201.msg294508#msg2945083. Download the .zip file that Illori made available from the link in that post and follow the instructions in that post of mine.
4. When you go back into the Bronze Doors Region, make sure you are in Third Person Follow camera Mode, and use the Page Down key to look down more onto your character so that the Waterfall is mostly out of the field of view... this will reduce the lag effect quite considerably.
Also, if you haven't done so click the Options Icon, then click Keys and set up Home Key for Zoom In and set up End Key for Zoom Out -these I find useful for use with theThird Person Follow camera Mode.
I am currently PlaneShifting using an Apple eMac 1.25GHz PowerPC G4 with 1 GB DDR SDRAM and running Mac OS X Version 10.3.9 and, although there is some lag experienced in the Bronze Doors Region, it seems to be far less than that which you've described as affecting your PS experience!
- my iMac is getting it's HD replaced under warranty and it's specs are in my sig.
- Hope this is helpful for you