Problem is that light fast road bikes don't take to dirt very well and are not suitable for long or even medium distance touring. You might do OK with a commuter style bike though.
I'm not a huge authority on this but there are some things I have learned over the years.
Bikes with suspensions are heavy. Knobbly tyres are great on dirt but just make the bike harder to push on pavement, plus the bikes they are on tend to be lower geared than road bikes and that means more spinning the pedals for the same distance. Slick tyres are good on pavement but not so good on dirt, the compromise has a fine tread on them. Some tyres are said to be "thorn proof" and come in three grades of that, the most expensive are the most resistant.
Light fast road bikes will generally have full carbon frame, or an alloy / titanium frame with carbon front forks. But they are no good for long distance touring if you have to carry your own luggage as they can collapse under the extra weight of tent, clothing, food and water. They may have no provision for mudguards / fenders. Carbon frames can collapse disastrously if the carbon is nicked or deeply scratched where a metal frame will give some indication of failure first.
In bikes without suspensions, steel frames are supposed to give a smoother ride than alloy, possibly because the steel flexes a little more. My boss is an former road and velodrome rider and does not own a car. He rides three different bikes regularly, one was built for him, another is an old Apollo, I don't recall what the third is, but they are all steel framed. He says the main difference between one bike and another is not so much the frame, it is the "group set" which is the brake and gear fittings. The Japanese made ones from Shimano are generally pretty good, but there is a variation in price among them and you get what you pay for. Campagnolo are similar, made in Italy and until recently thought to be better than anything the Japanese made, and are still considered pretty darn good.
For years the best quality bikes were supposed to be the Italian "Bianchi" models and they are still up there, cyclists in the know will salivate when they see one.
Bike frames are made in different sizes for people with different leg, arm and torso lengths. For instance, a lady's frame may be just as tall as a man's but it will probably be shorter as women tend to be shorter in the torso. If your bike saddle is so low that your knees are still well bent at the bottom of the pedal strokes, it's too low.
Another man I know has a recent Surly "Long Haul Trucker" which is a road bike made specially for long distance cycle touring. It has several points where luggage racks etc may be fitted and it can be fitted with mudguards / fenders which you will want if you are going cycle touring. Price is fairly high but not the most expensive I have seen. It has a pretty good review on-line, but it's not the only bike made for that kind of use.
If you are thinking of a French cycle trip, the roads will generally be fairly good, even off the major highways, the French started doing up their roads even before the motor car was invented. They have a big population in a fairly small country (compared to Canada, the USA or Australia) so can afford good roads.
Your best bet? You would be right about some bikes being bought, ridden a few times etc. Educate yourself a bit about what's been available, then start prowling the bike shops. (not K-Mart or Walmart) and tell them you are in the market for a good used whatever to suit your height and intended use. Leave a phone number, but don't expect them to have something ideal in stock just then. Most new bike shops with any kind of workshop attached will deal in good used bikes. I bought an Apollo about 5 years old then at a local shop for $200 and rode it to work for 16 years until some low-life stole it. B@stards
See the Sheldon Brown site for more information. Also go buy a few cycling magazines and read them, you'll learn a lot. Also google "veloculture" and "tweed run for some sidelights on cycle culture.