I'm currently running a Renthal o-ring, sprockets are getting a bit shagged though and I have been pondering the pro's and cons; o-ring a potential power loss but less maintainenance required, non o-ring a little more work, a little more power and a lot more chain lube splattered over my nice shiny back wheel
The Renthal chain has lasted pretty well to be honest, its done 8000 miles and still has some life in it.