I'd like to add to this if i may went through a similar issue, is a K&N / BMC worth it i think its great they can be cleaned and will save money over time that which is why i run one in my wifes commodore but its not for performance reasons.
My filter was filthy in my bike and couldn't decide whether to go stock again or go a Race filter K&N or BMC obviously if i got the later it would need a re tune cause the current map is for the stock filter.
Worst part about all this is there is very little solid data in regards to filters just alot of marketing talk.
So is sent a email K&N for some further info
"Hello,
I have a 2008 kawasaki zx-10r 1000cc with a full Yoshimura R77 a stock air filter and Powercommander 3 with a custom map to suit the above modifications.
My question is do you have any data or before and after dyno tests for your Race or normal filter to suit my bike.
I am currently weighing up whether to go wtih a stock filter or your Race filter but it depends on the gains in performance also remember the bike will be custom remapped to suit the new filter.
Kind Regards Jeff"
And the Response
"Dear Jeff,
Thank you for your interest in K&N products. K&N does not dyno test replacement air filters, street use or racing use. K&N only has dyno testing results for specific intake systems. I am unable to speak for the exact gains that you may experience due to the other modifications other than the amount of air flow that you will see with the K&N racing filter KA-1008R will be higher than the flow you will see with the normal air filter KA-1008 and very much higher than the stock disposable filter. this is due to the composition of the filter media used in our products. While a disposable is usually composed of a very restrictive paper or synthetic media, K&N filters such as the KA-1008 are composed of a 4-6 layer oil impregnated cotton gauze, and the KA-1008R is a non-oiled 2 layered cotton gauze designed for racing application only. If you would like to see mode details and information about our filters compared to stock disposables, please refer to our website
http://www.knfilters.com, or contact our customer service line 1-800-858-3333.
Thank you for writing,
Vincent Pistonetti
-Product Specialist-
VincentP@KNFilters.comK&N Engineering Inc.
http://www.knfilters.com"
From a performance standpoint knowing that k&n use the formula of if it flows x amount and filters x amount its bound to be better didn't really gel with me.
So after a month of trawling the internet i came up with the following conclusion:
Street filters can sometimes on certain models can lose power (Afr out or volumetric efficiency issues)
Race filters can at max pick 2HP but filter less, but no dyno proof of what it does to mid and low range (basically street use)
After seeing my old stock filter its obviously working, in the end i went for a stock kawa filter maybe if i did as many Kms on the bike as the Wife does in the car a washable filter would be beneficial, but not when i know that the stock filter can allow enough air to make 200HP with ram air and still filter all the crap out.
Hope this essay helps some one make a educated choice in the future.

Pretty clean inside

Kawasaki ZX-10R 2008 - R77 Yoshi full system, PC3 Custom Mapped, Benneli bar end mirrors, Puig Double Bubble, Radiator protector, CircuitOne Mirror blanks, Pazzo levers, Shift-I, etc