I have a Multiplus II (12V/3000W/120A - 230V) and have a really short cable run from the Multiplus to the Distributor. Victron recommend 2 x 50mm2 cable for both Positive and Negative (4 cables total) for runs upto 5m.
How are people connecting these to the distributor? Are you connecting 2 lugs to a single post on the Distributor? Or Can I use a single 95mm cable as opposed to 2 x 50mm Cable?
Using either one bigger or two thinner cables - both is an option. What is important that the cable size matches the load. Longer distance, more resistance in the cable = more diameter needed.
So as long as the diameter for your power draw and distance is met, using two thinner, or one thicker cable should not make a difference. Thicker cables become harder to handle/crimp, however - but the difficulty also depends on the equipment at hand.