The size of the rotor is only related to the total braking force insomuch as a larger rotor is required to dissipate the increased heat from a more effective caliper/pad. On its own, increased swept area doesn't create more braking force.
But only using my 08 as a track bike, I'd like to think I'd have some more rear brake should something happen to the fronts...
I tried it for giggles and I got more braking with engine braking than I did with the rear brakes!
Of course! And you should downshift and engine brake all the time.
If something happens to your front breaks - well, what if something happens to your engine, would you like to lag around a spare engine? ; ) The CBR is very lightweight and very well designed. For the track. And if you have any mechanical problem you are usually off the track very quickly, yes? ; )