I did a quick comparison for you on my 504 with the Dichromat head and Colour 500 computer. Using 20M and 20Y filtration the time difference with the 120 and 4x5 mixing boxes were as follows: 4x5 @ 9.2s 120 @ 5.2s That gives you a good idea of what to expect. I used to have a full service lab and I don't know of any exclusive 35mm mixing box ever made for the 504 or other Devere models.