i have to tell about my little experience with a great amount of ram...
I have a ultra expanded Amiga 4000 with a lot of ram. It's something like this:
1) 128 MB on the CSPPC
2) 16 MB on the MotherBoard
3) 64 MB on the Fastlane.
Total 208 MB of fastram.
But it's not that usable at all.
I mean, it's nice when I use Fusion beacuse I can give all the ram of a board to the Macintosh emulation, but if I try to run an application hungry of memory, just like ArtEffect, images comes out very very bad, block of colour in the wrong position... the image I get after some work of it is like a Picasso picture...
If I disable the memory on the fastlane everything is OK though.
So I believe that mixing memory is not that good, it's like amigaOS makes a great mess when it tries to handle such a big big amount of memory