I usually use between 50 to 60°. I'm no fan of the 3D cockpit and usually spend most of my time in glass cockpit view.
By the way - I thought human horizontal FOV was close to 180º, not 45º. I.e. you can perceive things almost at right angles either side of your head.
FOV is a generally misunderstood thingy.
Total human FOV is about 180.
When looking at the screen, imagine it's a window.
If it takes up 10º of your natural FOV, it should be 10º. If it takes 45º, 45º, etc. (Actually it might be 5º to 10º, etc., because the game is going off of a center to side for the º measurement, so it will be half)
Think about that until you "get it", and FOV will make more sense.
You can get a quick FOV estimate using the old astronomy technique of holding your clenched fist vertically and at arms length from you to measure the angle subtended vertically by the screen (ie the FOV). See http://www.oneminuteastronomer.com/860/measuring-sky/