Ask yourself how much would you ride off road and for how long.
If this is an itch, go scratch it and rent one. If the decision is keeping you up at night, make a list of reasons, pros/cons, and sum up your list. You already know what you're gonna do, you're just trying to understand why.
I've had the same thing happen with that damned S1! I love that bike!!!
I rode one and liked it more than I thought I would - crap, now what?
For me, it has to be which one would give me more pleasure all-around?
The answer was extremely easy to come up with - the K1600.
The S1 is a toy for the Hot Rocket Monkey that lives inside. It's not a comfort bike, not a 2up bike, gets worse gas mileage, has no radio, etc, etc, etc.
BTW - I'd love to have one of each.