What road bike would suit my criteria?
Sportive Cycling ? Is your country France perhaps.

Anyway, for longer rides and tougher exercise, it all depends what you mean by longer rides and tougher exercise.  

If by tougher exercise you mean more exertion then a vintage bike is perfect as it weighs more and you will get more exercise... or something. So save yourself the money and keep riding your current vintage bikes.

Personally I have a Bianchi Vertigo which I love.  The frame is carbon monocoque which makes it light and being carbon it means that I don't get as tired on longer rides and can recover faster to do more km's/miles the following day/s. That bike was a little more than your budget a couple of years ago, but you could easily pick up a full carbon bike for around your budget.