The screen is exactly the same as in the XPS13, meaning there's no turn off switch/option for the adaptive brightness.SOmewhat disappointing since the excuse for having it turned on in the XPS13 was that "by the time they have received feedback about it from the users they have already ordered the screens for the 2015 edition" (March 2015 to be specific).
It's also true Dell was extremely frugal when it came to processor power, my unit was actually configured with 4.5W on mains/4W on battery (43Wh here) with the usual 1 sec boost. Raising the power limit to 6W and undervolting by 90mV the m5 can sustain 1.9ghz dual core which is not bad I guess but the GPU will crash with undervolt over -25mV or so. Speaking of, can you look into the GPU performance? No matter what I only see a few peaks of 700-900MHz, it usually howers at 498MHz even when the CPU is not stressed at all. Very weird.
All in all, having used an XPS13 and now using a 7370 I do enjoy the latter much more for productivity tasks. Not perfect, but getting there. Is it "4%" worse than the MacBook? Yes and no; yes if you can't live with the screen or no, it's actually better if you can and are willing to tweak some power options when you need.