Well, I agree...
For some strange reason the vibration for a text message is always as long as the sound set for this event.
Only when you set the profile to "Vibrate" the vibration pattern is independend on the sound file.
The only solution I could find is to use the Vibro app. It allows for setting the vibration patterns for different system events. I have used it for some time, but it was long time ago and I don't remember if I had any problems with it. You have to test it for yourself.
Well thanks a lot Skrobel. It seems like it's solved, I think. But even if not, Vibro is a cool app. Thanks for the advice.