I've driven trucks with HX40s, modded HX40s, and a B1 equipped truck. About 2 weeks agao I drove a super 40 truck, and it is the closest thing to a B1 I've seen, but didn't have quite the topend boost.
All the HX40 trucks I've driven have been disappointing, but the Super 40 spooled great. If you floor it off idle it's awful, as is any big turbo, but rolling along and dipping into it it really gets going fast. If I thought it was big enough to support my new setup I'd have bought one already. I don't see why anyone would even consider an HX40 after having driven a truck with a Super 40.
For what it's worth the Super 40 I drove was on an 03 with injectors and a downloader. All the trucks I mentioned (4 with hx40s, 1 with a super 40, one with stock) are in the 350-400 hp range (my previous setup being the stocker @ about 350?). The B1 truck had about 550+hp (650 on a Mustang, but that was sketchy) and WAY more fuel.