All barrels are the same despite what anyone says to you. If you think about it, its just a metal tube thats smooth on the inside.
If you want to choose a new barrel, my advise is to choose one that you love the look of or if you want a really light one, choose a carbon fibre one like the Stiffi.
As for bore size, I use a 692/693 or bigger. When I use barrels with smaller bores, I don't notice any change in accuracy, but I do risk barrel breaks, and so I don't risk it. Up to you though