I bought a nice 30l Ogio tail bag, which is fantastic but obviously no good for two-up. Ogio makes companion saddlebags that collectively make a serious 3-piece kit that would hold weeks' worth of stuff. I'll probably end up with either that or the Givi hard panniers that Hitchcock has on the site. Those look solid. Each of the hard panniers is 20l and since they rest on a frame, they don't conflict with the pipes apparently. But they're not soft panniers, which is what the OP was asking about, I understand.
If (when) I get an Interceptor, I will probably go the same route that your taking. Hitting the NYC bike show today and will give it a more serious look.
9fingers