Absolutely no regrets here! I have been riding for about 25 years and spent 10 of those drag racing motorcycles in a semi pro class. I have owned several very, very powerful bikes and honestly i grew INTO my 300. Out of more than 20 motorcycles, i have never owned one I felt I would keep indefinitely until now.
For me it is the perfect balance of weight, power, comfort, ergonomics, styling, and ease of maintenance.
I rode the 500 also, but honestly, I was smiling bigger when I got back on the 300, so i went with my gut.
It's also a bonus that it happens to be the one my wife has most liked to tag along on. She swore off the R6 forever after 20 minutes sitting back there, and wasn't much for riding along on a few others. Now if I roll it out, I hear.....Am I going too? The bike gets along just fine with both of us.