Four cell and the 8/7 should be a good match, the 6.5X7 on a six cell should haul. What type of constant wattage is it rated at? You should be able to push 150% of the rated wattage for a couple of minutes anyhow with good cooling. I have done it with the cheap Out runner motors and they have held up without cooking a bearing or magnet, but they probably only have 3 or four hours each of total flight time. Stick with a real fast ESC when using a 6 pole motor (a good ESC with program limits will be able to survive frying the motor).
Edit to add:
Is your ESC a data logger that will really help you out.