The Nishiki Continental is sport touring bicycle with tyres (Kenda Kwest) I have found to be very slow rollers while the Cannondale is probably a higher performance machine and if you are running your tyres at 140 psi they had better be tubulars as this is far too high for most clinchers and most riders.

Slip some faster rolling rubber under the continental and get the position dialled in and your flat speeds should be very similar on both bicycles while the Cannondale might be slightly better on climbs... unless you are riding at a highly competitive level the difference in bike weight will be relatively meaningless.

As for lower psi tyres and speed... I have knocked down sub hour 40's on my vintage '55 Raleigh fixed gear that runs 26 by 1 1/4 tyres (597mm) at 70 psi... they have rather low rolling resistance and this was a bike that was once used for racing.

Or... keep the Continental as a comfortable distance bike and don't worry about the speed as much as you worry about enjoying the view while you ride what is a very nicely made bicycle and save the C'dale for speedier pursuits.