I am also considering a wheel upgrade for my Cannondale Tandem. We will definitely not race or have a real need for speed beyond our own fun seeking. I have not weighed the wheels on my tandem but they are a chunk. It also has what I consider a low quality shock absorbing stoker seatpost. An upgrade to Spinergy wheels would help us lose some rotating weight and improve ride quality so we can replace the shocker seatpost with titanium or carbon to further reduce weight and improve comfort for my stoker. Lower weight probably translates to higher speed and will make our bike better climber, significant given our Rocky Mountain environment.