How much proof do you need I'm wondering. You can drive those cheepos pretty hard. If you wire 2 of them in parallel how I mentioned before, you have effectively 0 chance of over driving them. Aside from that, their efficiency improves when they run cooler.
Really the only risk is cooling the...
I don't know why so many people have issues using these cheap Chinese Buck converters. If you are going to drive them above 50% of the rated continuous current, and you are concerned, double up. Give each of the a .1 Ohm resistor on the positive lead then connect the other side of each resistor...