My King is probably about 10 years old now, it works better and better with every year of use. Might have skipped on me in the last 5 years 3-4 times but never under load. However, that's an old King. Get a new one and you'll be in a world of shit. Bearings fall apart, axles break (even HD ones), the RD mechanism keeps skipping. Out of all my mates who have Kings, I have yet to come across a hub which works properly. They all hate them with a passion.
If you can get hold of a 2nd hand King (preferably pre ~2006) which has had many years of use on an XC bike then you might be in for a treat. Or else try to find one which has been used on a trials bike and has proven to be reliable. Otherwise forget it. I wouldn't swap my hub for 5 new ones, that's how bad they are now.