The B-115s are nice - but they will lose ability to comply a lot faster than the B-410s. I have both and although I like the 115s, they start bilabial fricatives at much lower volume.
I tend to keep my B-115s for smaller venues - because they seem really good at moving air at less than high volume.
As far as having four B-410s - that's all nice - but stacking them would require an OSHA inspection and permits. At 24" high each +casters or wheels, that stack'd be over 8 feet tall.
One second thought though -------------
One Barnyard BBQ I ran my B-410s in a stack
behind my B-810. Sonically it was nuclear and filled the whole valley with good clean bass.