Why place your heavy equipment up on a second floor? Sorry, this doesn't make any sense to me at all. T&G 3/4" ply is the way to go for your flooring. Better stability. I've seen a 1/4" hard board sheeting screwed & glued down on top of 3/4" ply as the final floor covering before. Works well.
I do have to agree, check your local building codes first!!
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