IMO, running water alone is not ideal in a modern, pressurized system on the street. Reason for that is, although water under pressure will not boil at 212 degrees, it will boil at a lower temp than antifreeze and create a sudden pressure spike, and plastic radiator tanks cant handle it. Todays antifreezes are made with anti surfactants, which help water absorb more heat. Water mixed with antifreeze, even as low as 20%, will help raise the boiling temp above the average running temp of the engine, thus reducing the chance of boil over and high steam pressures .
In the old days, before non pressurized systems, straight water was used without many issues during the warmer months, because the system wouldnt build up enough additional pressure if the water started to boil, and the radiators were two to three times larger in capacity than they are now, allowing for more water, which kept temps lower. Todays radiators only hold about 5x the amount water in the engine, which isnt as much as you might think, and so the system has to be in ideal shape or bad things start to happen fast.
Obviously, larger radiators will offer more protection. More importantly in modern cars with smaller radiators, smaller grilles, etc... adequate air flow, proper coolant mix and levels, and good water flow are also vital to keeping an engine running at the right temps, all yr long. Two fans will cool quicker than one, in most cases. But I think having one fan set to come on at 190 and the other to come on at 200 or 210 would work better than having them both kick on at the same time...because often, you dont need both working to cool the radiator, except in stop and go traffic situations.
