A quick once around the pattern may be fine at 4.8V but as I already mentioned, receiver dropout is a very real possibility.
I agree with this statement 100%. I would HIGHLY recommend that you not attempt a flight once your receiver pack hits 4.8 volts. Many receivers will start glitching at just below this voltage, and moving a couple of sticks at the same time will pull the voltage down quite a bit, even though it may come back up a little once you stop moving the sticks.
It just ain't worth the risk!
Stay safe.
Dennis-