Sorry, no answer from my side.
But have you checked Display brightness? @100% mine wouldn't reach 6hrs either, but at "normal" setting it's up to about 8hrs.
Have you tried running the built in battery report? There's a thread here explaining how to run it. It generates a report talking about mWh, so a measurable figure. It doesn't neccessarily tell you anything about the uptime, but it should tell you, if your battery is within it's specs (42mWh)