Just a note that TDP doesn't equate 1 to 1 with power draw - it's a largely made up metric to approximate max heat generation out of the box that is only really comparable within the same product line. A 3900x could in an extreme case have less power draw than a 3600 (depending how hard you're working the cpu).Low TDP is one of my primary "must haves" when buying a new CPU, so a 65watt 3900 would be awesome. I run my PC 17-18 hours a day 7 days a week, which consumes a ton of power. A savings of 40watts not only means the CPU uses less power, but means less cooling, using even less power. The savings add up.
But how does it compare to lower range CPU's that suck down more power? There would be no point in buying a 3700X if the 3900 is both faster AND uses less power.