Oops, I got distracted by the later discussion. I've had the Q605 up to 260 MB of RAM by installing a SIMM doubler in the SIMM socket wtih two 128 MB SIMMs + 4 MB on board = 256 + 4 = 260. So the Firmware (Mac folk call it firmware instead of BIOS, but it's just a nomenclature thing) supports at least that much RAM. You can't close the lid with a SIMM double installed though.
You could probably just run a line from the SIMM socket's address lines to supply the address lines which the 4 MB is missing and take that memory up to 64 MB using 16M X x parts. The Samsung 16M X 4 parts are fairly convenient to use for this purpose, but they are physically too large to fit where the existing 4 MB is located.
To go beyond 64 MB, I"m pretty sure you'll need to find another RAS line you can use to make the on-board memory double banked.
Because you seem to have a lot of experience with this stuff, if you see anything obviously wrong in my earlier post, I'd appreciate a correction. There are still some holes in my understanding of how RAS and CAS were typically arranged on these older machines.