How long is too long for interconnects?

I have a strange setup with my integrated amp in a recess behind my wall-mounted TV above the fireplace.  My equipment rack with my digital and analog sources sits in the right corner of the room connected with 5m (16.4ft) rca cables. My tower speakers sit on each side of the fireplace with approx 12 ft speaker cables. I have had zero issues with interference, noise or hum. I was particular when running my interconnects to avoid contact with any power cables which might contribute but I wouldn't be concerned with longer interconnects or speaker cables to a reasonable point.

Long speaker cables are worse than long xlr cables. RCA also has restrictions for maximum length. XLR is the preferred way to hook up all equipment using long lengths and/or your equipment is balanced. Also, very short speaker cables aren’t good either. I remember reading years ago that there is a minimum Length like 4’ or more and then a Recommended maximum length. 

I recommend longer ICs and shorter speaker cables after much trial and error. The best budget ICs are Blue Jean Cables LC-1. Low capacitance, shielded and cold welded connectors. Buy equal lengths (not custom) and try them. You can return them but I still use them for stereo and HT including 15’ runs. Well built and well priced. 

+1 on BJC LC-1

@GK:  Too Funny!  😝