The answer is not. I've read on this forum and on r6messagenet.com, that the stock air filter flows better than the K&N. If you're gonna get an aftermarket air filter, get the BMC race. You can get them at kneedraggers.com
I put a K&N on mine and i can't tell the difference in power but i can tell a big difference with my throttle control and the bike seems to run a lot better with the K&N versus the stock filter, and as far as price they adverage around here anyway a little over $70.00
I think the general consensus has been stick with a stock filter on the carbed bikes unless you plan on jetting as well but with the FI bikes, the ECU will compensate for the greater airflow or you can adjust it via a PC3 as well.
man this topic is old.........penfold is right, if you not planning on new exhaust and/or jetting, maybe a K&N filter is not as effective...in other words if your bike is mostly stock might as well leave it that way K&N aint gonna help. i personally have only seen success with the K&N's (00 with full akra exhaust and jetted) and they are a superior filter. other than that i dont know about other after market filters....im sure they are good as well.