I play at 800DPI. and 800 ingame
It depends on how you feel comfortable using 803 sensitivity with 800 dpi, I use a logitech mouse and my mousepad is 45x40cm.
In-Game mouse sensitivity and mouse DPI are two different variables in the equation. That's why you will hear various answers from many different individuals. Find what works for you and stick to it, if you constantly change your sensitivity you will only hinder yourself when it comes to natural point of aim.