There is a way to make turboprops just as silent as jets inside. Airbus had some concept design a few years back. But basically, just do what Piaggio did with the P180 – put the engines in the back. That thing is conversation quiet inside the cabin at FL350. When I hitched my ride we flew without headsets for the entire cruise portion and the pilot talked to the people in the back without problem.
When we’re talking long haul passenger turboprop, are we talking Tu114 speed or commuter plane speed? The former one is almost in jet territory, speed-wise. Flight duration should therefore not be an issue. And with airlines buying smaller planes (exactly how many A380s are in the air at this particular moment?) the slightly longer times can maybe be compensated with more direct routes which again will save more fuel.
Tackling a problem that isn’t there?
How efficient is a TU-95 vs a 777 or even later designs like 787/350?
High bypass turbofans with giant „props“ are similar to turboprops already in the way that almost all thrust is created by the large fan in front (compared to turbojets of the old times using exhaust gas out the back).
Turboprops would mean a little less fuel burned for a longer time.
Tu-114/Tu-95 aren’t up to today’s standards on so many counts (including noise) that we can simply disregard them. On the other hand, it would be interesting to look at Airbus A400M and the Ukrainian AN-70 vs. jets of comparable size and configuration.
A400M, is like everything military, a financial nightmare. Tech wise it’s interesting, but probably not a major improvement to the PW150.
first use a train for e.g. London-Barcelona
If there was a decent sleeper service on a route like that, I would use a train journey like that over CAT every single time. Unfortunately most of the sleeper services have gone away. (I have a friend in the computer demoscene, he lives in Oxford and goes to demoparties all over Europe (including European Russia), never using the airlines. A few years ago he used to be able to do a lot of them on sleeper trains – but not so much now).