I not worked with ORWO DK 5, but I made enough experiments with positive and dup positive films b&w.
Find here "ORWO formulaic - photografic instuction for processing of materials" - Edition 1982 - 5 DK data. http://www.dump.ro/poze/dk-5-a-jpg/21013 http://www.dump.ro/poze/dk-5-b-jpg/21014
I make same tests with Orwo DP 3 fresh and expired in 1986. Photographic differences were not found major.
http://www.filmotec.de/English_Site/...-TI-DP3e_5.pdf (ORWO duplicating Positive Film DP 3)
A picture made with three fresh DP. http://www.dump.ro/poze/orwo-dp-3-jpg/21012
I make same test with positive b&w Kodak 5302.
This materials have a sensitivity 3-6 ISO, according to developer procedure.
I make test and with POTA developer.