I bale a lot of  native hay in some  extremely  steep hills.   I either  have to   ride the brake all the way down, (which  can get really hairy when one wheel decides  to   either; skid, or  turn backwards.   Especially  true when the  clay ground is hard as cement, and  the lugs  can't bite.) 

Anybody  who has baled  prairie hay  knows what I'm talking about  on  how  'slick'  the hay is..  I call it  'summer  toboggan ride'. 

That's  why I went with a  Mfwd  tractor a few years ago to  help out  with keeping the  dang thing under control.    I usually  have all 4  tires locked up (diff lock front and rear, plus the  4wd)    for  the  steeper  sections, and try to   go uphill on the steepest windrows.   The worst that could happen is  I'd spin out going uphill.

This  has  most of my  concerns  other  than the   run-away  of going downhill.   Over revving the engine is one thing.. but  when it gets  going too fast and the tractor starts hopping... that is when it gets  'fun'.     The hopping part  isn't  much of an issue  since I switched  tractors from the 4430.   Over speeding   the engine still  is.

I could downshift to some  ridiculous  low gear..  downshifting  at least  4 gears  is  when   I can  finally  feel  the engine hold me back.   At a whopping  3 mph.   That won't fly.   Riding the brake isn't the best either...  for   crap getting in the system.  

  Don't have to  be real aggressive with the brake, as long as I stay ahead of the speed..  which can mean  sometimes  riding the brake for up to a 1/4 mile.

So,   you guys  who have installed a  exhaust brake on their pickups, what is your opinion on how effective they are?  I don't know how to compare  exhaust brake to  percent of  actual braking power..   10,20,30,40%??  

Maybe the  manufactures of  the  exhaust brake  have  a  'typical'  brake or  load against the engine  that could give me  an idea.