Ishiwata quad butted tubes came in several tubesets... my friend has a Kuwahara Club Sport road bike that curbs in at under 21 pounds (lighter tubeset) with a Shimano 600 group and my Kuwahara Cascade has the heavier quad butted tube set but it's still a fairly light bike that rides wonderfully.

Ride quality has so much more to do with geometry and other factors like wheels and tyres and in this Kuwahara made a very nice bicycle.