If you took the same rider and gave them seat time to get comfortable on both an 899 and 1299, and compared lap times on a "normal" track (not Road America, Cota, etc. - long/fast tracks), here's what I think you'd see:
TRACK DAY riders (not professional racers):
The slowest 10% of riders would be faster on the 1299
The middle 80% of riders would be faster on the 899
the fastest 10% of riders would be faster on the 1299
Now that I've gone back and forth (from 1199 to 899 to 1199R frankenbike) I can firmly confirm in firm terms, firmly, that the 899 is a sweet package for the track and much easier to ride fast than the "big" bike is. I would venture to guess I'm in that fastest 10% bracket, but even still it takes a lot of work to get the advantage from the big bike to where you can go faster on it than the 899. Braking and setting up a good smooth fast corner entry from 170mph is immensely more difficult than doing it from 150mph, and most people will tend to over brake from 170 and have a slower corner entry than they would from 150. That translates into 10ths every time, every corner, the faster straight away speeds actually hurt your corner entry speeds. Same thing goes for getting on the throttle at the apex, it's easier to get on the throttle earlier and harder in the turn on a lower HP bike. The big bike wants to stand up and wheelie out of the turn, which is very difficult to control, which translates into slower initial exit speed. The big bike can make up some time in acceleration but usually not enough unless the rider is really capable of using the power before the bike is fully upright. Might sound easy, but it's not, and electronics can only do so much to help with it. TC can keep the rear from spinning up on the exit, but it won't keep you from running wide if you can't steer the bike on the throttle while still leaned over. That takes good bike control, body position, weighting the pegs, etc.
