grouping of varieties in orchard rows

I am planting about 100 trees next spring. I will have about 20 different varieties. For the disease-free varieties I plan to plant them all in the same row. I am wondering about the rest. For example, if I have 5 golden russets should I plant them in the same row next to each other ? Should I disperse them throughout the same row? Or perhaps should I plant them in different rows, in different parts (my little orchard does slope and one spot is a little damper than most of the orchard)?

Sincerely, Peter Drevniok
Wakefield, Quebec zone 5

A very incomplete answer, based on personal experience: Do not separate varieties throughout the orchard. Each cultivar ripens at a different time, and chasing all around the orchard to find, and pick all the Belle de Boskoops together is no fun. You will have quite enough difficulty keeping track of where the Boskoops are in the first place without trying to search through the entire orchard for each instance. It becomes more problematic deciding what to do when one of the Boskoop trees in the middle of the block dies, and you set about replacing it with a new cultivar - too many such random replacements and you end up with chaos again. (I got some scion wood from a very old, local Seek No Further tree last year. This is now successfully grafted onto rootstocks at opposite corners of the orchard, because there happened to be gaps in the rows at that time.)

Broomholm Orchard
Zone 5b in Nova Scotia