Once you put your circuit together, add a form of Tabata HIIT to it. The one I am currently doing has 10 exercises per cycle and goes for 10 cycles. Each cycle goes for different lengths of time, for example the exercises in the first cycle may go for 15 seconds each with a 10 second break between cycles, the next cycle may have each exercise going for 40 seconds with a 15 second break etc. You can use the workout that NattyShirts put up and add planks, jumping, pushups, sit-ups, uppercuts, body shots on the bag, etc. The aim is to keep the intensity up, and dont worry about the power yet, concentrate on speed.
Good luck and have fun.