For serial
interfaces check out:
http://www.cmdweb.com/cbm
And check out the "Turbo232 High-Speed Modem Interface". With a SuperCPU you
can go to 115200 bps.
But, but BUT! that's a cartridge and doesn't do anything with the serial IEC
interface. However, it is an excellent device. Even a plain-jane C64 can
manage a 56k modem at full speed with one.
Really!?! I was always told (or read) that a 64 needed a SuperCPU to get
over 38400 bps.
Bryan