The seat has arrived yesterday.
Did my first 1 hour ride today. It is clearly not enough time to say if Wunderlich solved my pain on long rides but I have to say it showed much better support then OEM and I feel that my weight is now spread over much larger area. The seat is much harder then OEM so I don't feel that I'm sinking into it.
One important note:
When I had OEM seat installed, I had to put it on high at the front and on low at the rear to stop it pushing me towards the tank. When swapped to Wunderlich, I left the same settings on, and it caused the problem with the lock. The key would turn left easily to unlock rider's seat, just as it should, but it had huge resistance turning right to unlock pillion seat. I thought something was wrong with new seat and I knew it can't stay that way because I was going to break something trying to unlock the pillion seat. However, I went for a ride and new seat was now pushing me away from the tank. So, I stopped, carefully unlocked both seats (I was really afraid the key would break) and adjusted it leveled on low, both front and rear. Now it was right, I was perfectly leveled and whichever position in the seat I wanted to take, it wasn't pushing me forwards or backwards. When I arrived home, I tried the key in the lock again and it was working perfectly smooth.
So, the conclusion is, Wunderlich seat can't be installed with rear low and front high as it would jam the latch on the lock.
So, even if the pain comes back, I feel much better with this seat. For me it was money well spent.