Since you asked - wisdom may be found in just one word
"KARATA"
Need more...please read this link
http://www.bigdogbiker.com/forums/drive-train/5979-karata-part-i.html
Have a 07 - K9, have installed, removed and re-installed the 4" Karata open primary and only have praise (I will have another post as to why the re-install - nothing to do with the open primary itself). There is a ton I have learnt in the process and I can vouch for the engineering that goes into making the Karata. All considered it is $$ well spent and you do GET what you pay for.
Some IMPORTANT POINTS:
* It is a RSD open primary. (All mgf. do NOT make them)
* You have a choice 2.5, 3, 4 and 5 inch (the 4" adds HP, not sure how much but I CAN FEEL the DIFFERENCE and PULL):up: :up:
* The Piranha clutch is IT:up: . NO MORE trying to find neutral, switching gears is like butter...:lol: :lol:
* You have a choice of OBS (outer bearing support) one to suite your style and bike
* SINGLE piece back plate...no one and I believe NO ONE other than KARATA has this. (with the later models the starter is completely concealed, giving it a CLEAN look)
* Easy and perfect install - all you need is a wrench and I use an "impact gun" recommended. (In reading Gas (Chris') install I remember him having a difficult time when installing the open primary..had to remove the tranny...Gas please chime in, I may be wrong)
* American built and sturdy as a horse. Not going out of business like other competitors
* Always in stock and ready to ship
* Jim, Mr. Karata himself - GREAT CUSTOMER SERVICE :up: :up:
There you have it....need more feel free to PM me. Basically you can't go wrong with the KARATA, that's my opinion and more.