Given the total supported RAM memory is half what you suggest, indicates other performance
or maintenance could be done to help the computer; or consider a Mercury Legacy Pro SSD:
http://eshop.macsales.com/shop/SSD/OWC/Mercury_Legacy_Pro
There are two models of 1.67GHz CPU PPC 17-inch PowerBook G4, and yours would seem
to be last model. The earlier one cannot use DDR2. Here's RAM spec from MacTracker for yours:
• PowerBook G4 (17-inch Double-Layer SD) 1.67GHz:
Maximum Memory 2.0 GB
Memory Slots 2 - PC2-4200 DDR2 200-pin SO-DIMM (running at 333 MHz)
Introduced October 2005
Discontinued April 2006
Model Identifier PowerBook5,9
Model Number A1139
Order Number M9970LL/A
Graphics Card ATI Mobility Radeon 9700
Graphics Memory 128 MB DDR
{This model would have been the one shipped with the Double Layer SuperDrive
the G4 processor was left alone from the previous version 17-inch build model}
Do you have a professional performance testing software, or some other means to verify
the change of these chips to an unsupported quantity? (compared to? in original, or other
poor replacement quality) Sometimes a new matching pair of correct spec RAM can be
better than an older build of similar spec RAM. The population of chips on the RAM card
could be of higher quality on a new card.
The Graphics Memory number is not affected by the total system memory population in this.
An aside to the idea of simply doubling the RAM total, does not work on most PowerPC Macs.
Or most others. So while it may appear to have helped in your instance, I'd not recommend it.
Everymac.com, mactracker.ca, among others do not suggest that doubling the RAM will work.
The OWC macsales.com site and crucial.com sites both have correct quality memory to
match up with correctly identified build model Macs. The suggested and recommended
route for performance issues, is to become aware of all the contributing factors. When the
correct spec memory is at the total supported (tested/guaranteed by reputable reseller) the
other option would be to consider an SSD for use in the older ATA/IDE (PATA) system.
Curious that you've seen some improvement by simply doubling RAM over supported totals.
Virtual Memory, hard drive free space used by temp swap files, usually is the other factor.
In any event...
Good luck & happy computing!