I was reading that some are able (through some standard modification) to take 256MB of RAM.
I isn`t that easy, you need to upgrade some chips on the Fastlane (no, not just the ROM that holds the z3scsi.device). Those chips are nearly impossible to get today. I asked DCE but they said they don`t have then either. Thomas Dellert wanted to turn to some ex P5 people at BPlan and ask them....never heard of him since then.
I assume that there are only about 10-20 of those "golden" Fastlanes worldwide. Even if you manage to get one of those (I have been searching for years now) you still will have to pay a hillarious price for those 8bit 16 MB Modules. I have seen a set of 4 going up to about 100 EUR (they seem to be useful in old MAC-Servers thats why prices are so hight plus there were only few made, `cos at that time PS2 RAM became popular)
But haveing some extra 64 MB RAM with those cheap 4MB 8bit modules isn`t bad either. The RAM ist dead slow (about 90% of A4000 motherboard RAM) but still faster then haveing to use some vitual memmory hack when opening large pictures.