5 is highly optimistic. Real world average efficiency is closer to 2.5 (lower in colder climates) because there are a lot of variables you have to get exactly right to hit that 5 COP, and they very rarely line up.

Source: I have a Fujitsu 36K BTU cold climate 4-zone system installed two years ago to replace electric baseboard heat. [1]

[1] - http://www.fujitsugeneral.com/us/products/multi/2-3-4rooms/a...