Listen flat bars are OK for mountain biking but are very uncomfortable for road and it will sit you up too much, not leaned over, aerodynamic. And if you are doing a century, you'll want to be able to move your hands and body around more than a flat bar will offer. Stay away from a Mustache bar. Hard to handle and very uncomfortable on longer rides.

I guess you are looking for a cross bike but get one (and they usually come this way) with regular road bars. Bianci does make a nice cross bike as does Lemond.

My take, you really can't get a bike that does all. Pick a sport. Buy the bike that fits that sport. You can always take a road bike on dirt trails if you use a wider, computer like tire. If you buy a cross, computer, comfort, sport, mountain bike, they aren't really suited for road riding. If you see yourself doing more trail, off-raod riding then get a mountain bike - hardtail - and an extra set of wheels that you can use for roading.