Thanks for the response Bret. Those are good insights. Especially the part about the panniers. Unfortunately, it's hard to assume the rack capacity from the pannier capacity.
On previous bents I've used both under seat racks and behind the seat racks. As you mentioned, the under seat racks are more stable. I've gravitated to behind the seat racks and paniers when possible. Aerodynamics is one of the major advantages to bents. So, I prefer to have the panniers draft behind my seat rather than hang below where they create more resistance.
While I'm not expecting a loaded Q45 to be a performance racer, anything that can help when facing a relentless headwind can be greatly beneficial. This is not the case if it is not reliable or can't really hold much weight.
Could a C.B. staff member please pipe in here on the rack capacity?