Road bike for brevets Until today I've been doing 200km brevets on a trekking bike. It was quite comfortable, there was no ass pain after that, but the average speed was low (24km/h). Also if the wind blew, I had problems riding further, or arms were aching from taking more aerodynamic position. 

So I bought a road bike, and it's great, but after doing 50km on it:
- ass pain became unbearable (I had pants with a gel diaper)
- my back and shoulders were aching from road bike position

Is road bike really a good choice for 200km brevets or longer?

Triban 520 c1:
Riding long distances comfortably has very little to do with whether you're on a 'road' frame or a 'trekking' frame and much more to do with the tires you're using and the seat you're sitting on. Wide, plush tires will go a long ways toward absorbing the bumps in the road, and the seat is your most important point of contact with the bike.

For starters, try swapping the seat from one frame to the other, swap out the tires for wider touring tires, and see if your problems don't go away.

Edit: and for Pete's sake, make sure the bike fits you. If it doesn't fit you, nothing else really matters. Have a professional fit performed if you need to.