Some of the single cabs were great, BF Super Twin for example, and some were a bit lacking like the Hartke HyDrive 410. I didn't get the chance to try adding another Hydrive to see what happened.
Practically I like a modular set up so I can carry a lower weight when I don't need more cones.
The Marshall VBC412 was great on it's own though. Epic as a pair. Interestingly as those are 4ohm cabs I would often use 2 amps at the same time. They were EQ'd differently when I ran a split signal set up with clean deep lows on one and all the drive and FX on the other.
Even when EQ-ing them differently they still worked together better than the Markbass 2x10+1x15 set up.
Someone with far better understanding of maths than me will have to explain that!