Richardco,

the problem simply is the "wait for sync" and "receive data" routine.

the data you will miss is the one that is being transmitted by other talkers while you are busy receiving data from the one talker.
(you can't receive from more than one talker at a time)

Letting the PIC do some work on the data once it has been received will not cause any timing issues.
You can do as much as program space and memory allows.