Uh, no. With underdriven pulleys the accessories turn slower for a given RPM. If you slow the engine down, you also slow down the production of heat. It's the relationship between the engine speed and the water pump speed that's important.
So then if I drive 10% slower with more throttle it will overheat? :D
Good thing we never have to go up hills.
I realize slower RPM's with higher load creates more heat but it doesn't fly as a reason for overheating issue's.
