Sawzall. 9 inch grinder would be very cumbersome to work with in this application. Are you using a cut off wheel in your grinder? Mine is a 4 1/2 inch, if yours is only a 4 this could be a problem. Get a heavy duty 4 1/4 inch electric angle grinder with a cut off wheel and it will zip right through it. I persononally would prefer the sawzall though.
