My first bike was KLR until it was stolen :spank:
I went with FZ6 and I don't regret it for a second (i do want to buy a klr 650 though as a second bike as i loved it).
I have not ridden FZ1, but coming from KLR650, i had to get used to the amount of power of FZ6. There is a little of working the throttle there, but nowhere near what was needed on KLR. I'm 6'3, 230 and i didnt have any problem with posture/ergonomics - FZ6 is still very upright. I didn't even get bar raisers, only upgraded the seat (Spencer's seat mod)
The reason why I want to have both FZ6 and KLR650 is that they are different bikes. I miss the ADV look, the height (sometimes, but again, it's not as big of an issue), fork travel and laughing at the potholes - FZ6 definitely takes it harder. FZ6 is definitely just as customizable.
If know it's easier to say than to do, but I'd recommend (if your finances allow) getting FZ6 AND keeping klr ;-)