While I do not question that a given 3Rensho can be faster than a given Colnago, the described ride seems to fall more into the "placebo" category.
Whenever I ride a new bike, it just seems to fly. No matter which bike it is. Even my old beater Alan cyclocross bike seems so stiff and so fast after I haven't used it for a few months! (I am sure somebody will explain that frames get soft with use and "reset" after a rest.)
In the end, on a quality hand-built bike, barring any serious mechanical problem, performance differences (for a given rider) probably mostly are due to fit, comfort, handling and similar issues. My bikes are fast if they allow me to pedal efficiently, without back, shoulder and other pains distracting. Handling: you can go fast if you don't have work hard to keep the bike on the road...
From that perspective, maybe the 3Rensho does fit better - I see many people on bikes that are too small.
The exception to the above is magic. If a builder somehow induces some magic into a bike (and while you may laugh, I do not dispute that this could happen), it will fly. But unfortunately, the few bikes I had that I thought were magic, did lose their magic when it came to the "race of truth." In time trials, I found my times to be very consistent, magic bike or not. A 1972 Cinelli Supercorsa, repainted in forest green, came to mind. It just seemed to go. But then I put on aero bars and entered a time trial (my Marinoni had been crashed and was part of a pending insurance settlement), and the results were disappointing. I fear Cino would not have approved of the bars...
The placebo effect should not be underestimated, though. I find it extremely hard to go fast on a bike I don't like, while looking down at a Cinelli decal (old style, of course), just makes me want to go faster and harder.
Of course, your experience may vary.
Jan Heine, Seattle