I run the gauze that comes with the airbox, but the roads are very clean here, not much dust, etc. Mostly just insects in the summer.
I've heard of people modifying to use a K&N filter, but that may make your bike run a little richer if air flow is reduced at higher revs.
Let's ask Duckhunter, he will probably have done the research on this...
Or do a search and let us know what you find.
Euro RC51 SP2: HRC WSB Ti Hi-Level, T1 Airbox & Snorkel, PCIII, Dymag CA5 Carbon Wheels, Ti64 Spindles (F, R & Swing Arm), Mori Link, Maxton GP7 Shock & Ohlins 832 Forks, Brembo GP Calipers & SBK narrow track (F), Braketech Disc (R), Brembo billet Underslung x 2 Brembo RCS, Tyga Triple, 7075 Stem, Probolt Titanium all over, Babyface rearsets, MR Complete Carbon Lineup, Custom Undertail & CBR 1000 LED, Watsen LED Indicators, Harris Brace, Giles clip-ons, Corbin seat, etc. 2013 BOTY.