Capn Bloggs,
Forgot to mention (busy with the Senate) that a handy page for you to contemplate is page 4.7 of the Performance Engineers Manual (Andy has it!) which gives you the Gross GA Climb Gradient (OEI, A/C Off, Gear Up, F18 and with icing corrections) as a function of airport Pressure Altitude and Ambient Temp, weight and airspeed.
Unfortunately, it is in pounds...
Stay Alive,