You've got something running in the background, did you check the Sype Video, and disable it entirely (Messaging App->Settings)?
What happens if you go to Settings->System->BatteryInfo->BatteryUsage? What apps are at the top, and what percentages?
My 950XL does pretty well on 420, not as good as 318, but I easily get a day, sometimes almost 2 if use is light.
I have seen the odd "blacking out" thing a few times, and once I had a series of "so dim it was as bad as blacked-out", but it went away after a couple of soft-resets, fortunately.
I would agree that 420 seems to be a step backwards, in some respects, really awaiting the next Release Preview or Release build...