I still have the (heavy) dual exhaust in my shed, never got around to putting it on... I'm thinking of getting a new frame for the Bandit and look for some new suspension parts and wheels. That little 400 stills has speed records in the smaller curves that I haven't been able to beat with the old Gixxer lol
Anyway, the best exhaust I've found for the B4 is the Yoshimura steel exhaust. It's very light, gives all the ground clearance you will ever need and it breathes pretty good even up to 15000 revs. I've also ran a GSXR 400 4-in-1 exhaust, didn't really like it. I went back to my stock stainless headers until I got the yosh pipes. The Yoshimura end can is pretty bad by the way, better to replace it for a simple open muffler.