Hi James:
in the attached file are some data I´ve collected from the RcTimer page (links included). Also u can play with your particular data of weight in the Excel table. Aparently, each 5010 motor can take a bit more of 1Kg, depending of propeller, battery etc.
For instance, in your case of 3.6 Kg, u need 600g/motor, a total of 350watt. As a rough estimatin, you´ll get 12 min flight time with a 5000, 4s batt.
I´m just finishing a quad with this motors also (see progress here: viewtopic.php?f=25&t=2926)
Hope this helps you
Angel