All last season I used Dura Ace chains and could never even get 2,000 miles out of them before they were too stretched and needed to be replaced.
I've been riding with the SRAM chain that came with my Force group since late Feb (over 4,000 miles) and it's still shifting flawlessly and has not stretched enough to be replaced.
My LBS mechanic said he's had similar experiece with other riders.
When I need to replace it I'll definitely stay with SRAM.