We're bouncing around here.
You've identified three issues so far-
- Underdrive pulley on the water pump
- Standard water pump mismatched to pulley ratio
- temp switch instead of a controller
I would fix those issues before doing anything else. You should either drive the water pump 1:1 with a high flow (8 blade) water pump
or 1.4:1 with a standard 6 blade water pump. Matching your pump and pulley ratio alone has the potential to make a huge difference. Then get a better fan controller, if you even still need it.
