Have an 08 Pitbull and like most, road conditions play the largest role in the comfort of the ride. Also depends on personal tolerance. I put the drop seat on and removed the factory spring one and actually like it better, due to the fact you are sitting down more and have sort of a "stop" behind you that keeps you secure. When I had the factory spring seat, there were several times when I found myself being sucked towards the back of the bike when getting on the throttle good. Only issues around here are usually transition areas going onto bridges where the pavement meets up with a concrete bridge. Seems like there is always a hump there so I just brace for it and raise a little pressure up off my rear and absorb it as best I can. Sometimes one will slip up on you and give you a good jarring, but so be it. The bike looks awesome and just like about everything else in the world, it is just a sort of trade off.
As for you Germanbiker, I don't have any experience in "bumpy curves" as most of our roads that are traveled at higher speeds are smooth. My suggestion would be to just take it slow and easy the first few times and get a feel for each specific road condition. I'm sure you will be riding familiar roads after a while so you will know what you can and can't do. Heck, it is different here in Texas as opposed to Sturgis! Here, if a curve gives you a speed limit of say 45, you can easily go 55 without any danger, they are just cautious. In Sturgis, if they said 35, that was the MAX you wanted to try!
All I can say is have fun while you look good on your Pit, but ride safe and smart!