In 42 years of ownership of my Norton I have always got long life and milage out of my chains, I use just heavy duty chains but the way to get long life out of any chain is maintenance, every oil change I will take my chain off while the motor oil is draining I have a spare chain that I join to the bike chain to run it off and put it on the sprocket, once off I will soak it in kero for a few hours, give it a really good clean and check for any tight spots, tight spots are a chain killer, any tight spots found I will work them free with more cleaning once they are free again I will then soak the chain in hot gearbox oil, be care full when heating the oil, then let the chain soak over night, I have been doing this ever since owning my Norton it comes from my dirt bike days.
I normally get over 40,000 miles out of a chain, my last chain is one of Andy's chains and expect to get even longer life out of it doing this, by the way Andy is a great person to deal with he sent my my new chain to Aussie land even before I payed for it as he was going away when I ordered it, not to many business men around like that these days, so order one of Andy's chains and you will have no problems at all.
Ashley