I know there are many choices in batteries, BUT............ I fly at 6500 feet All my friend use lipoly but NOT me. My slow stick uses AAA's NiMh, 8 cells (9.6Volts) this give me 20% more tork. I tune the motor, which is another simple gain of 20% more. And use a 12/8 prop, we have thin air.
You can charge faster, the cells are cheaper, if you solder your own battery pack you can have 3 pack for the cost of 1 lipoopy, I flew 8 hours Indoor with 3 pack one day, swap & charger. and I'm still on my first OEM motor.
Although I broke a prop or two I feel this is a very good record for the NiMh flyers.