Bulldogge - does your SPectrum have drops? I think it did, in which case I would not go Constructeur, I'd go low riders or a rear rack. I'm finding my drops interfere with the porteur (granted it's larger) and I can't put much on it. There are some really cool more race bike oriented racks that Tubus makes, but they're spendy. They have a ti one I love.

http://www.tubus.com/en/rear-carriers/airy