I went with the whole enchilada on my 85C, less the extended firing pin, and am glad I did. I too run with my Kadet 1/2 the time.
You'll need to run a heavier hammer spring with the Kadet kit than with 9mm and you'll lose some of the niceness in DA because of that, but the SA will still be amazing. It's no big deal to change out a hammer spring to get all the benefit back.
The race hammer and sear give the biggest bang as far as improving the trigger. It will remove all the creep, not pre-travel, and make the hammer stop camming back in SA.