At 20MHz, 4800 @ 4MHz become 24000 baud. Yes, a new baud rate option would be needed - an oscillator used or multiplier option would be my preference.
I've never exhaustively tested this code ( <A href='http://www.mev.co.uk/vbbaud.htm' Target=_Blank>External Web Link</a> ) but it seemed to work. Increasing the baud rate from 4800 started to introduce errors (4800*1.03).
I've never got my own Terminal program into a decent enough shape to release in public, but as I'll undoubtedly also have to make it work at these weird baud rates I'll look at doing that.