I, too, have come to the conclusion that Peak Global is the best of the coolants that are not factory specific. With regard to percentages, the AMSOIL chart lists the capacity of coolant in engines. When you loosen the bottom tap on the radiator, let's say about 1/2 of the total drains out. When you refill with water and run the engine, the resulting mix is about 50% fresh water to 50% old mix. Do it again, and it is about 25% old. Again, and it is 12.5% old. Do it five times and there will be about 3% of the old mix left. Even then, what is drained will still be tinted with the color of the coolant. If less than 1/2 the capacity drains from the radiator, it will take more flushes to get the old mix lower. After doing this in a couple cars, I have also come to the conclusion that is is a lot easier to drain and refill every couple of years, even if you have a "lifetime" coolant.
Mark