You definately want to be circulating the water all the time as the hot spots are near the exhost valves and on big V engines the intake manifolds are usually heated with water as well. Have the fan off should not be a problem as the heater will probably dissapate enough of the heat on a cold day - make sure you turn it to outside "cold" air for max cooling. Bigger engines generate a lot more heat so cooling may become an issue if it is not really cold outside. Only really good way to tell is to try it where you can stop if it overheats or at least coast at idle to allow it to cool down - less throttle makes a lot less heat. When I ran my full grill block I didn't have a problem until I got going over 40mph then the bigger gas consumption kicks in and the heat goes up.
The system also incorporates an electric water pump, which, unlike the conventional belt-driven water pump, is driven only on demand, and at variable speeds, avoiding inefficient and unnecessary overspeed running. Mechanical energy savings, optimum temperature control and fast warm-up from start offer the potential for additional CO2 emissions benefits.
BMW is now using new electrical coolant pumps in its straight-six engines. The electrical pumps operating exactly?and only?when required, meaning that they develop their maximum output and performance only at high and very high speeds. They remain passive immediately after the engine has been started, ensuring in this way that the engine is warmed up more quickly. This alone helps to reduce fuel consumption in the EU homologation test by approximately 2%.
The e-pump would be great but the only problem I see is cost. Most of the after market ones I've seen have a life cycle of 2000-2500 hours at a cost of $250-600, and thats with a self install, so the 12,000 a year driver would be replacing them every 5 years.
Using a sensor you jam into the radiator it varies the voltage sent to fan so you are not either on full low or full high but at the right speed for a given temp. I have one waiting to be installed on the Jeep with a fan out of a Taurus, same principle should work for the water pump.