@Piru
I don't think there's any Amiga turboboard out there that handles more than 256MB ram (BPPC) but the AmiJoe supposedly could take 512MB.
When looking at that there's not reported any chip mem so it's quite obvious something is up.
Anyway, as far as I know the Amiga can theoreticaly take up to 4GB memory so nothing there to stop you from inserting a hole bunch of those 128MB Zorro cards to boost your memory.
So I'd say on a classic Amiga the maximum fastram would be 256MB on BPPC + 7 * 128MB on Zorro = 1152MB memory.