50' feet is ideal I think. You want to chill your wort down as fast as you can in most cases(the exception would be an extended hop stand for an IPA at varying tempatures). If you wanted to, you could make a prechiller that you place in icewater out of 20 feet, then make the rest for the wort chiller for the wort. That way you are running not just tap water through the wort chiller, but you are running ice water. If it were me I might actually think about doing that. Otherwise 50 feet is not overkill for a 5 gallon batch.