20 is good, 20 is pretty optimal and something I'm aiming for. Just need to exit some positions first.
In my opinion, 5 is way too low and would leave me seriously under-exposed. There are more than 5 sectors with a lot going on and I want to hold at least the alpha plays + few beta plays in trending sectors.
But I guess at the end of the day it's very subjective and depends on how much time we each have to put into research and management.