Paul, you keeping the Factory Water Temp Gauge? If so, why have another one? Its not that important to know the exact temperature of your Coolant.

I would personally put the need for Gauges in this order........

1. Boost
2. Oil Pressure
3. EGT
4. Fuel Pressure
5. Oil Temperature
6. Water Temperature

That doesn't mean I would have all of them.

But, Tony has spoken some sense. The more Gauges you have, the more there is to watch, which can be a real pain and most of them are just academic, incase something goes wrong. Often I find that my Gauges behaving the same way every single time I take the car out almost become part of the scenery and I wonder if I would definately notice something going wrong in time to even have an effect on it.