Load a Minimax, set it to max # of voices, this should fill a significant amount of your dsps.
if it didn't fill dsp #9 load another instance, set to a high voice count
did it break on #9 ? probably not

set one instance of minimax to a # of voices that fill (say) 8 dsps.
according to your hypothesis the next masterverb pro will break on the memory of chip #9
did it break ? I bet not...
btw Masterverb Pro's don't count for benchmarking - use Masterverbs instead to receive comparable results - MV Pro is an optional device.
I guess it's significantly more demanding, so your 7 instances are probably very good.
regarding the logic:
reverbs are built from delay lines
delay lines need memory - some on chip, some over the PCI bus
both resources are limited
you'll never need that much instances of a top reverb - it's simply a waste of resources.
No human ear will be able to distinguish them in a production - in other words: you could achieve the same result with less demanding devices.
there's the solo singer and the background vocals - the solo Stradivarious and the violin section. There is a reason to isolate the 'better' performer

cheers, tom