Unfortunately there is no research that compares the capacity of a give-way line and that of a stopline in the context of a PICADY junction. The difference may however be minimal if drivers continue to regard the junctions as give-ways. Furthermore, it is likely that any effect on capacity will be negligible in the very situations where it is necessary to assess capacity in the first place (when the RFC is high), as most of the traffic will be moving off from a queued position.
If using PICADY to assess a junction that has stoplines instead of give-way lines, all you can really do is to model the junction as usual and then assume that the real capacity will be slightly lower, i.e., the PICADY results will be on the optimistic side (everything else being equal).