What road bike would suit my criteria? I own two bikes, both are vintage. Steel frames with 700C wheels, friction downtube shifting, drop bars, toe clips. One is more speedy with less comfort (fixed gear conversion), the other leans more towards commuting/cyclocross (touring).

I've recently been really wanting to get into more serious road cycling and/or cyclocross after re-starting riding bicycles this year. So far I've looked at many brands and models available to me where I live, and I'm still really unsure. I'm currently settling with Trek Madone 3.1, full carbon, used, but really cheap. It has a mix of SRAM and Shimano (105 I think) on there. I'd say my budget is somewhere between 700 to 1000 US dollars, that value is converted. Definitely not looking for anything professional, but for something that still at least has a carbon fork.

I already have fine commuters, this I need mainly for tougher exercise and recreational long-distance riding and maybe as an extra fast commuter, but not for racing, since in my country the road conditions are pretty bad and sportive cycling is rather unpopular (except for CX).

I'm also looking at B'Twin, Bianchi, Author, Boardman, Merida, Vitus, Raleigh, and some others.
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.