The gnarly is a low end pipe and my bike had stock reeds with platinum pipe when I got it so I put a gnarly pipe on it with moose read spacer (spacer installed for mid to top so I put it between reed cage and carb not against intake) and I installed the boyeson pro series carbon fiber reeds in the stock reed cage with stock reed stops.
http://www.jcmotors.com/p-3649-fmf-gnarly-2-stroke-exhaust-pipe-kawasaki-kx500-88-04-desert-pipe.aspx It really woke the bike up and with the proper jetting (previous owner had it very rich) the throttle response is fantastic I always knew when my 500s were running right when I could just putt along in 1st 2nd or 3rd and twist the throttle and the bike revs instantly with no hesitation or sputter it just revs and goes.
Before the mods and proper jetting the bike was slow to respond and didn't have the arm stretching pull I wanted in mid to top end and I really can't say which mods did what since I changed everything at once to include taking the carb apart and cleaning it real good and setting my float level but I really like the combo.
So the gnarly is going to give you more low end grunt and the boyeson reeds give better throttle response then the moose spacer gives more mid to top where I have it installed but I figured with the gnarly pipe I had all the low end that I would need and I'm glad I went the route that I did.
I would love to see the rad valve and v-force compared to the stock reed cage with the boyeson carbon fiber pro reeds to see which one is making more power and at what rpm because I have had rad valves in my previous k5s and wasn't all that happy with it's performance so that just leaves the v-force that I haven't ever owned but you might want to try the boyeson pro reeds with stock cage and stops with moose spacer and gnarly just to see where you are at and it's only $50 delivered for the reeds instead of $170 for the v-force.
I'll be honest with you, this bike pulls extremely hard out of the hole and I can't imagine being any happier with the way it pulls through the mid range to top end it's just a lot of fun to ride.
http://compare.ebay.com/like/290485474026?var=lv<yp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y