I moved from a 55 to a 125, and it was a pain but not impossible. I used a 10 gallon, and 3 large plastic tubs and a couple big plastic trash cans. I only used about 25 gallons of existing water, new sand, and all my live rock.
Typical process, water from tank into tubs, seperate corals and rock into tubs, fish and invertsand into to 10 gallon. I had about 90 gallons of rodi
mixed and heated ready to go. Everything out moved 55 and stand out, moved 125 in. Got plumbing all set, sump ready over night. Next added sand, added water, tested system. Once all good, added rock, let run, got temp and salinity good tested water, water good, added everything back.
Took all weekend, long days but my goal was to minimize time in tubs away from lights. 2-3 days isn't a problem, I'd be a little concerned if it was much longer.
It can be done, the key to success is having everything ready to go. Good luck.
125 gl (72.5x18.5x22), 33 breeder tank sump, 3 maxspect led, Diablo protein skimmer, 1"live sand base, 175lbs live rock, 2 Orange Clowns, 1 yellow tang, lawnmower blenny,several mushrooms and leather corals, a couple small acro's and a standard cuc. Tank transferred from 55 on 24 Dec 2011