Most PC serial ports will run at 230400 baud.
The J53 will... just set:
BRG16=1
BRGH=0
SPBRGH=0
SPBRG=5

That might shave it down to under 4 hrs.
Make sure the MAX232 (or whatever you're using) supports 230K baud... some transceivers don't.

If I were sending that much data I'd be inclined to use a transfer protocol like XMODEM or something.
Are you just blasting 256MB out the pic uart and hoping the PC will keep up?