Someotimes you can tune yourself out of contention. As for me if the 600 isn't fast enough your not riding it right or you need to save up some coin and trade it for a 750 or 1000
Really i have seen bikes with a 10-15 hp deficeit own bigger faster better prepared but poorly ridden machines. And I am thinking the small advantage you would get in the mid range or in transition from low to hi rpm would be very neglible and something you could mask easier and with less effort with proper gearing...