Well, I am sure that niceguy will have a problem with me(a girl) answering this, but he can kiss my butt.

Having excessive sex should not hurt anything. You may get sore, or get to the point where you cannot get off, but after a day or two of resting you will be fine.

Also, I think everyone, male or female, gets off faster when masturbating then during intercourse. I believe it is just because we know our bodies better than anyone else ever could and we know how to do it right! When masturbating you don't have to worry about pleasing anyone else, you just get the job done. Why waste time?