Hi Greg,

It definitely speeds things up going from 4 to 20MHz. Instruction cycle time will be 5x faster than with 4MHz. I'm not sure if the ICD part is 5x faster, but you'll definitely notice a big improvement in ICD speed.

Make sure to program the PIC with one of the MCS loader firmware .hex files for 20MHz, and to add DEFINE OSC 20 to your programs when using 20MHz loader/crystal.