i keep a 150,125,75,47,20,20 and my new 210G all on my 2nd floor old old house wood floors... we are going to reinforce the floor under the 210 but only b.c it would make me sleep better.
Personally If your concerned I'de stick w/ a 55 or 75. I have a 40 breeder,37T, both on stands. and 2 20's and 2 10's on metal double stands. all in my bedroom on the 2nds story and we have a full basement. my dad doesn't want me to get anything larger.. the 2 20s over 200 lbs each and my planted tank is one of them w/ 5" of gravel/planting substrate thats about 20+x3 lbs a bag... so about 500lbs on a 24 X 12 footprint? and the stand has 4 weight bearing narrow points. The tanks are spread out along my walls the 2 doubles are on a weight bearing outter wall. when I set them up I didn't really thhink about this all.. but now.. lol... he's better off letting me get rid of the 2 doubles and putting a 125 up here.. if the floor isn't bad from those 20's.. It shoudln't have a problem w/ the 125.
and to help w/ any possible leaks do a leak test before bringing it upstairs. should always do a leak tets on any tank new or used imo.. thats alot of water.. for a lil' extra work.