For me this is what I got before:

600 4 cell pack

x5 7 mins flight on standard servos (3003, 112 etc), on sportman flying style, x5 is pushing it a little

1,100 5 cell pack

x6 7 min flights on high torque servos (645, 5645), flying mild 3D

If in doubt just get a voltwatch ... its worth every cent as sometimes we forget or the battery is about to kick the bucket. Mot of the times I stick to about 4 flights on a fresh pack. Can't go wrong with that