You have to keep in mind that brifters perform 2 different and unrelated functions. They shift gears and they actuate the brake callipers. Your brake callipers don't care if you have a double or a triple front derailleur and crank. Shimano 5700 and 5800 series brake callipers use the same cable pull ratio and SLR-EV architecture. Your brake callipers are a non series version of the 105 5700 brakes. "Upgrading" to a 5800 calliper will make very little difference to braking power, you would get more for your money by installing better aftermarket brake pads. There may be small incremental improvements between 5700 brake callipers and 5800 brakes, but there will be no night and day difference. The biggest functional difference between 5700 series brakes and 5800 series brakes is that the latter have a low friction coating on the brake wires that reduces braking effort . Changing your brake cables to the new standard would also be a cost effective way to upgrade your brakes