I would normally use the PC only when there is small table that can be placed right near the look up subroutine. Another consideration is whether or not you are using the DPTR at the same time in a loop or other type of processing algorithm. For example, if you were scanning a buffer in XRAM using DPTR and had need to translate byte values through a lookup table in the CODE space then the use of the PC relative addressing can save quite a number of cycles in the loop.

Michael Karas