I have a G3 B&W 450. System 9.2.2 and OS 10.2.3. I cannot get two or more 256 Mb ram modules to work together. Any time two or more modules are use I get freezes. There is no way to predict when the freezes will occur. The problem is so serious that it makes OS 10.2.3 useless.
If one 256 Mb module is used, there are no freezes. I can use two 128 Mb modules installed in any pair of slots without serious problems.
I have used three pair of cheap ($25) modules from OWC. All were advertised by OWC as appropriate for the G3 B&W. I have used two ($50) pair from Fry's. None worked.
Finally, I have used a pair of Kingston ($70) modules from Mac Mall. They were shown by Mac Mall and the Kingston web site as being specific for the B&W (KTA-G3100/256). They worked no better than the others.
TechTool Pro was used to check all modules. TechTool Pro has ten different ram tests. If the modules are tested one at a time, each one passed all ten tests. When tested in sets of two, three or four, they always fail at least one to three of the tests. (Arpeggio, Web, or Leap) The tests were not consistent. The modules did not always fail the same test.
Each module also passed the DIMM First Aid test.