let me throw in my 2 cents that 99.9% of the bacteria is living in your substrate, your filter, and other items in the tank. there is almost nothing floating in the water itself. use the water to fill up the new tank simply for the sake of saving water, but it won't do much for preventing a cycle.
however like others said, by transferring your substrate and especially those cansiters (make sure you don't let anything dry out) you definetly won't have a problem with a cycle. you *might* get a mini-cyle, but nothing on a large scale.
and tygger, from his description i would say he's moving everything into the 120.