The Anniversary Update isn't out yet, so Opera's power-saving mode is probably the best you can get at the moment.

Actually the tests in the post linked from the Edge blog we're on current stable bits; Brandon's post details additional improvements coming soon. In our testing we're considerably more efficient than Opera.

Notably, Opera turned on their (off-by-default) ad blocker for their power efficiency measurements.

Trying to get a full days use out of my laptop I did some tests last week, Edge with adblock beats Opera with battery saver + adblock.