I've been shooting panoramics with the 43mm lens on the Mamiya 7 for fifteen years now. I love the camera for all other types of shooting as well, but the 43mm paired with the pano adapter is a great combination. While it saddens me to see it, you can pick up a M7 body and the 43mm for a fraction of the original retail cost. I've never done any enlargements bigger than 14" wide, but they look great at that size.
I can't offer any opinion on the XPan, but I've never had a significant complaint about the Mamiya 7 system. Good luck.