guess it depends on how well it's designed and built too
I'm rethinking this... I have 2 50's, but to fill a 50gal with snails seems like a bit of a waste. I need a new dresser, and I have a space 44" wide for it, so I think I'm going to build a stand that holds one tank, some supplies, and has drawers beneath it. I'll get a cheap ass 20gal for snails.
I built this earlier this year, but you'll need more strength than this. Simple re-design of this stand half lapping the cross beams under the tank shelves might do it. I know you're thinking of scrapping the stack idea, but just in case....