Welcome! I think you'll like the ZX6R. At 36, you're probably mature enough to make more reasonable decisions about speed, behavior, and appropriate places to enjoy the capabilities of the bike.
I personally think that taking the couple hundred bucks for the slip-on is probably better spent on a trackday or one-day riding school, but to each their own. I know the sound with the slip on is a lot nicer than the stock buzz. That said, I have a dual Two Brothers exhaust on mine. It came that way, but I love it compared to stock. So I say one thing, but I would want a slip on for my bike, too.
Never ride faster than you can stop