What's your intended purpose for this rifle? Games gun? SERIOUS training? What's going to be your average round count per year?
If it's going to be a once a month range gun, that sees less than 3000-5000 rounds a year, or something you're going to use for 3 gun, you'd probably be suited for the DD as its lighter, and will do just fine in every aspect. It'll be just as fine if your plan on shooting more than that.
If you're going to be putting 15000 rounds down range a year, going to training classes, essentially gettin down and dirty with the gun and getting it all kinds of Canadian f**cked up, go with the KAC. The SR-15, in my opinion, only shines when you use it as it was intended. As a tool.
The SR-15 is worth the additional 1400 in every aspect, if you need it or require it, but it will not make you a better shooter. Although you might get some brownie points for range cool, or on Instagram (if that's your gig). I would spend some time and clarify what you plan on doing with this rifle. All look-cool-factor, and "proprietary designs" aside, what you want to do with it will dictate which rifle you should purchase far more efficiently than most anyone's opinions.