I'd say put in modern off the shelf PC rams like 2x1GB and limit it at 512MB which is the Amiga limit. That way the accelerator would be cheaper (crazy, innit?), a soldered on special SRAM would be hard to replace if it went bad.
But yeah Prowler is right, it's all to easy to start dreaming of the Ultimate Amiga eh?
I've said my piece and will shut up now.