I think the key is not if you legally can but should you? I know where I am at, I see aircraft all the time flying at what looks to be 500-700ft. Since legally they can be flying at 500ft, some might. They move very fast and for you to get out of the way, especially when you get over 400ft line of sight becomes more difficult, it is just not worth the risk. Think about it, if you hit an aircraft and actually cause that aircraft to be downed, is it really worth the lives you endangered? Also, if more people start going over the 400ft limit and shared airspace with airplanes and helicopters, new laws and restrictions will be put on us making it even harder to fly legally.