The main difference is that most 600s are gutless down low so if you don't carry max speed through a turn (slow, look, lean, roll) the bottom end tq of the FJR *can* make a difference.
So, in reality, the difference is limited to track use when there's no x-ray vision to see what's around that next curve.
600s are not gutless "down low" because down low is different.
Down low for an R6 is 10,000 rpm 1500 below its peak torque number. While its peak horsepower is found at 14,500 rpm.
You dont need to carry max speed through a turn you need to be in the correct gear for the turn.
An R6 can enter the turn at the same speed as an FJR but it will have higher mid corner speed due to its lighter weight and will accelerate away from the FJR on exit due to it better power to weight ratio.
This will happen on any corner on any road that the rider is willing to ride hard.
You can not say street speeds are lower and closer to the FJRs limit therefor the performance advantage of the R6 is negated. That is because the percent of handling performance remains the constant. If the FJR executes a corner at 75% of capacity and the R6 executes the same corner at the same 75% of capacity the R6 will win every time.
Lets say you restrict the entire corner speed to make it easier for the FJR to compete at legal speeds.
You would need to set some criteria for measuring a winner. Lets pick hitting specific marks as the measurement.
Even at the same entry speed, mid corner speed and exit speed the lighter and better power to weight ratio the R6 will be much easier to consistently hit the marks with. Every time. Thus the R6 is better at street speeds where there is "No X-ray vision" because of its lower weight and better P/W ratio available for mid corner corrections.
The R6 is better in every measurable performance category in every scenario. Its the immeasurable catagories the FJR is better. Like comfort, long distance amenities.
Given the same rider skill.