This may be helpful. I have 5800 levers and BB-7 road calipers on my commuter bike. I've read that from a brake lever cable pull perspective, 5700 and 5800 brakes are mutually compatible.

The brake response isn't as crisp as with 105 rim brakes, that's for certain. But I will say that my disc braking on the commuter is adequate even when the bike is loaded. I try to set the cable tension with as much "pre-load" on the disc caliper arm as I can manage without rotor rub. And I'm fussy, so I'll spend the time truing the rotor so that I can set the pads close.

From your description of "sliver" of light on each side of the rotor, I can't tell how closely you have them set up. Good luck. Phil