If I need something that precise, I assume it's for something expensive. So I buy 2 cheap 8' 2x4s, screw a stop block to one of them, clamp it to the mitre fence, and use the other 2x4 as a test piece to confirm I have the correct length. But my mite saw came with roller extensions like this:
so supporting the 2x4 "fence" 6' out isn't a problem.
[This message has been edited by agnerd (edited 12/6/2013 10:01a).]