Sparky,
Contrary to popular belief among some, longer shotgun barrels do NOT give higher velocity NOR do they give tighter patterns. They do provide more weight out front which helps some people swing smoother. If you like muzzle heavy shotguns, go for longer barrel. If you like quicker swinging shotguns for faster reaction in getting on the bird, go for shorter barrel. I shoot 26" barrels in O/U's and they are lightning quick. The BPS receiver will add several extra inches over the O/U but my choice would be 26" or 28". Can't see any benefit to longer barrel unless you are shooting a lot of trap.
Good shooting and be safe.
LB