It's really a matter of personal preference mixed in with what you're using as standard insulation. I think 50 is about as low as I've gone. I did that fully dressed in a summer weight bag with a bag liner. I had a foam pad, but I threw it out of the hammock because I found it unwieldy (not because I wasn't cold). In preparation for nights that might be that cold in the future, I got a slightly warmer, synthetic bag, and I picked up the Super Shelter. I haven't had an opportunity to try these out yet, but I decided that it was worth some money to guard against a cold night of sleeping.
If 50 degrees was going to be a regular occurrence, I would invest in some kind of insulation (obviously, because that's what I did), but if it's going to be an anomaly, maybe just investigate your pad options for those nights.