I personally stay at or below 1800 mah in the AA size NiMH as a battery expert said that they are less fragile internally compared with the higher capacity cells.

If you have only used NiCADS and rely on a voltmeter to alert you to the low battery/time to stop flying time do be aware that NiMHcells hold their voltage right to the end then you get a very short period of time when it drops rapidly. In my case I have my tranny alarm set to 9.3 volts and get less than 4 minutes to shut down. In other words if it beeps I land on the next circuit and shut the engine down on the field immediately.