I am with Ravi on this one, so I would say, go with something in the middle 20lb, the thing about good braid is the dia is small and you will not get "line memory" so no twists. The thin dia will allow you to cast distances where mono of the same breaking strain would not allow you to.
The problem with using long leaders is it will hamper your casting if you are joining them with a swivel and it will damage your tip guide because you will knock the tip guide with the swivel while fishing. My personal opinion is that long leaders for Barra are an unnecessary over kill, I use very long leaders when fishing over reefs for GT. You can use long leaders and join them to your braid with knots to get over this problem, but I do not trust braid and mono knots however here's one which works http://www.youtube.com/watch?v=clHNRQ2drBg
The reason I used to use long leaders for Barra and Ravas in the past was more as a “shock leader” because I wanted to use mono of a thin diameter to cast further and I did not trust the light mono to take the pressure of a heavy spoon when casting.