Jumping in the fray here to share my experiences...I have done most of my miles on early 750k's with the stock brakes and they are way better than the twin leading shoe drum on a cb350 twin. This season, I have been riding a 750f3 with the stock triple discs and the addition of braided stainless brake lines. This bike stops wayyyyy better. Period. Please note that the f3 still has 35mm forks and for all intensive purposes the same frame as the early k's. The forks have not collapsed. The frame has not noticeably wobbled. You still are not doing stoppies. And I have never managed to lock the front wheel on any of these bikes on clean dry pavement with reasonable tires, ever. The back brake on all of these bikes will lock easily and unpredictabally, causing the rear to try and overtake the front, leading to the nearly inevitable and always painful high side...thus the back brake must be used with moderation. My 550? Stops pretty damn good as it has nearly as much brake as a 750, yet 80 some odd pounds lighter. I considered swapping the 750 front brake with a drilled rotor, but sold it before I ever got around to it.
Have not been caught in the rain on the f3 yet. However, if it is as bad as the 550 and early 750k brakes in the wet, the discs are getting drilled, period. These brakes are pure terror in the rain.
