Snes MAD-1, EX-Highrom, and EX-Lowrom mappers max memory space? Support writes?

Super Nintendo MAD-1, Ex-Highrom and Ex-Lowrom mapper-decoder support writes if ROM is swapped for RAM? What is the maximum space these allow?

Where can I source detailed information on these and other mappers-decoders? I'm looking for at least 8 megabytes of buffer with 70ns RAM. If someone can help me find a commonly available mapper-decoder for this that'd be great.

Anyone here do Snes Playstation prototype development?

Looking for a supported reproduction mapper available to assemble a RAM cartridge for Sega 32X CD homebrew development. Thought it'd be okay to ask here since Snes seems to have more hardware mappers-decoders available with reproduction cartridge support. Sega implemented a 315-5755 mapper but unfortunately is not in reproduction and Everdrive carts don't seem to support extension RAM with this mapper for CD title development (only backup saving seems supported and krikkz hasn't responded to me).

Thanks for any support