In defence of "bike boom" French equipment:
I have used a Huret Allvit on my friend's 1957 René Herse tandem. This has the drive off the front, so a very long chain, potentially a problematic setup. It shifted great, at all times, uphill, downhill, whatever. The consensus in France is that the Allvit is ugly, but works wonderfully. Singer didn't get over the ugliness, while Herse spec'd them on his "bijoux" bikes, including racing bikes!
Haven't tried the Huret Jubilee yet, but a bike is waiting in the garage for the weather to clear. Generally, Herse and Singer did not spec stuff that didn't work. There are plenty of Campy NR-equipped Singers, but Ernest Csuka feels the Campy won't work well with large cogs, so he prefers the Huret. On his personal bike, he has at least 100,000 km on a Huret Jubilee, and he claims it is the same derailleur since the early 1970s, when he chucked the Nivex (the bike dates from 1956 or so). There was some national pride (or was it that the guys in the bike industry all knew and helped each other), but if something didn't work, it wasn't used. An exception are Japanese parts - Csuka avoids those at all costs. Mostly, he is resentful what happened to the French bike industry. The Japanese do things better, but they don't offer the choices that a "constructeur" like Singer needs.
Many of the bike boom bikes cut corners where they could. That includes poor cables, dry assembly, poorly made "accessories" like rims, freewheels, etc. All of these will affect shifting, more than the components used.
The much-maligned Mafac brakes fall into the same category. For years, we thought the bike boom bikes stopped poorly because the Mafac centerpulls were no good. Only recently did most of us discover that the brakes are great, when set up correctly.
For the front clamp of the Jubilee - that may be why Singer always brazed on a nifty little piece and converted the clamp-on front to one that mounts on braze-ons.
Mark (Petry) - your new Singer has a Jubilee rear. Does it shift OK?
Jan Heine, Seattle (all bikes I regularly use have Mafac centerpull brakes these days)