Oh yep. If you under drive the water pump you are killing flow, especially and low engine speeds.
If you are shifting at 8000 or something you MAY be able to slow the pump down to help keep the belts on. If you can keep the belts on, then you still overdrive the pump.
The little bit of power you save under driving the pump you lose that and then some because you can't really control coolant temp. Anytime the engine temp gets over 180 you start giving up power.
160 is way better, but it's hard to get the engine that cool. You also need a very good, light grade oil.
