I used the information specificallhy available on Tech Specs for the Constituion class around the internet...
Now there's your problem!
If you can site sources where the Constitution class ships regularly travelled faster than any starship in TNG, DS9 or Voy, please do...
Oh, that's trivial. Warp eight was supposed to be hair-raising at first, but our heroes never faced ill effects from doing it - and, as in that above video link, in "That Which Survives" it got them across a thousand lightyears in a day. For Picard, such speeds were supernatural: seven thousand lightyears in "Q Who?" would take three years rather than a week.
Naturally, "That Which Survives" has always been an outlier. But it's also an example of regular performance, as opposed to alien-induced speeds or other flukes. And outliers are the norm for TNG and VOY as well, more or less requiring us to believe that the speed corresponding to a given warp factor varies per unknown circumstances. Whatever the explanation, the phenomenon itself completely negates the value of any calculations on what these mighty starships "could" or "couldn't" have achieved. What they did onscreen was
possible for them, leaving (in good or bad) basically nothing impossible.