Macintosh with 24bit ROM in theory can access up to 16MB address space. But in reality, it has to leave some reserved memory address maps to frame buffer, I/O and ROM.
To access more RAM, you may need additional software with patch. See the info I found: http://lowendmac.com/2015/32-bit-addres ... lder-macs/
My physical Mac SE with a 68030 acceleration card can access more virtual memory in disk through SCSI2SD. TBH, SD is faster than physical memory.
Recently, I'm working on 24 bit ROM in BII. To avoid overwrite in memory, I limit BII memory to 4MB. Things are kind of working now for 24bit ROM under System 6:
1. Fix frame buffer
2. Enable SDL
3. Fix emulated hard drive
Once my PR #136 and #136 are accepted, you can give a try.