If you have the money, are responsible and safe, and can ride an R6 proficiently, you'll be just fine on a 1299. That said, if you aren't really confident, and have never been in situations where you've had to save slides, dodge things, or any other of the things that happen riding that you just can't practice, an expensive big bore bike might not be the wisest platform on which to experience those things for the first time. Same as why pilots get lots of hours on cheap trainers before they are turned loose so they don't bore a hole in the ground with a $100M jet.
Also consider that something like the 899 is much better suited to traffic and slower riding. When you are on an 1199/1299, and you get anywhere near cars or traffic, you feel like a shark desperate to keep enough speed up to get cooling. If you have ready access to high-speed canyons or backroads, no problem, but they are not all that much fun just trolling around. My 899 has much better manners, but will still power-wheelie in 2nd gear. That's plenty for the street, I think. An 899 with about another $3k invested in suspension upgrades, and my brake fix (pratically free) listed in the 899 section gets you within 1 second of the 1199 on the track. My 899 usually pulls with 1198' and R1's on the track. You obviously get left down the straights by 1199's and HP4's. As an owner of almost every iteration of the bike, I have no prejudice in saying that I think most people would be quite happy owning an 899 if riding was your primary goal. If you just want the biggest baddest thing, that's different. Another thought. The dealer her has sold quite a few 899's, but very precious few of them have come back to be sold used, so people must like them. If you got one, rode it a while, got some experience and then decided it wasn't powerful enough, I don't think you'd take much of a beating trading it back in on a 1299.