since we have some 08+ guys chiming in, ill clear this up.
for the 04-07 go with the bmc filter ONLY. there were fitment issues with the k&n on these bikes. if you are not running a full system, stick with the street filter. the stock ecu can still compensate enough to not have to worry about any remapping.
if you are running an 08+ either the bmc or k&n will do fine. the k&n is a bit cheaper so if you are worried about cash outlay, go that route.
if you are running a full system on any of your bikes, you will need to get it mapped again. use the race filter for any full system (or more) setup.
that being said, if you plan on keeping your bike for a while its always a good idea to get an aftermarket, cleanable filter after the first 3000 miles. you will save $$$ in the long run. even going with the race filter will not allow any particle large enough to harm your engine past it.
if you are expecting any hp gains, dont expect anything. a filter is there to clean the air going into the motor. the amount of airflow between the oem and race filter is minimal (except on bike like the r6 that have options for very minimal screening from bmc).
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