From what I could find in the past when this idea has come up it is better than stock but not as good as a cone type filter. See the air box is still more restrictive than the cone filter and the air box pipe at the bottom is only 2.5 inch in diamter. A cone type filter with a 3 inch pipe diameter will flow the best. How much hp and air flow are we talking between stock vs cut box vs cone? Not much. A typical cone filter with 3 inch pipe will only yeild about 3hp over stock but will flow much nicer at high rpms. I say cut the stock box if you want but it would be better to go with a cone filter. In both situations the filter is going to be exposed to the elements meaning rain and dirt so why not just go with the cone set up that will flow better. The only compromise I could see is removing the stock box top while using some sort of way to hold the filter in, then on rainy days you can easily slap the stock top back on to protect the filter. This will give you a nice compromise of air flow and safety from rain. Another alternative is to use the cone filter with a very short pipe to hide the filter as much as possible behind the turn signal and possibly use a heat shield from a K&N fipk. By placing it behind the turn signal and using a heat shield you can block it from any rain and large dirt particles. On the other hand this also may cut down on air flow to the filter. In short you have to figure out what works best for you. The cone will flow the best but if you live in a really dusty area or rain area the stock box with a drop in filter may be best.