I ride my Marin Treviso (neuron steel) with a bit heavier wheelset and heavier training rubber on my weekday rides (except hillclimb day). It weighs in at 19.75 lbs.
I ride my sworks tarmac on the weekends - not really super light - 18.2 lbs, but better wheels and rubber.
I do ride a higher gear and faster on the tarmac, and it feels great after being on Old Iron all week.
Why not ride the tarmac all the time?
Good tires ain;t cheap, good wheels ain;t cheap.
I'd rather not trash wheels and tires when I bump around by my lonesome...
When I ride with the younger guyz, the tarmac comes out cause I need all the help I can get.
I ride an alu frame Marin w/ Forte Titans on Hillclimb Tue. cause my sweat eats thru anything else... and I sweat buckets on hillclimb tue.
Titans are heavy, but they freighttrain on the descent - and that's what I'm about...