I would base the battery size more on weight than electrical capacity... I would never fly a 600mahr pack when the weight of a 2300 pack is almost the same.

I never fly 4.8 batteries ... I have switched entirely to 6 volt 5 cell batteries. More head room before a brownout. One crash due to batteries and you will start thinking the same.

I never run a NiMH down to zero. When the charger says I have put 2600 mahr into a 2300 mahr battery (example), I know that it cannot be because of losses and heat produced, therefore when I put 1800 mahr into a 2300 mahr battery I know that did not happen either.

I know weight is important, but flying safely with more battery power than necessary is more important.