You don't switch the fans off the coolant temp in the radiator, not if you do it properly. You put the switch in the head, which always runs a good amount of degrees hotter.
I don't agree that at speed the fans should not come on at all, if they do your radiator core is too small, the airflow is insufficient or there's some other issue (like late timing). See you are reasoning that the mech fan is needed at speed but it's not, in fact the fan partially freewheeling in there possible isn't doing much at all, the airflow from driving will easily be overcoming the pulling power of the fan. The fan only becomes efficient when the engine bay is hot enough for the thermo clutch to lock it and at low speed where it actually helps draw air through the radiator. For the rest of the time it's just wasting energy.
Because of this your reasoning that the clutch fan will maintain a lower radiator core temperature will not hold water IMO. The other factors greatly overpower the ability of the fan to pull air through at speed and as such at when comparing both at the same speed the core temperature would be about the same.
Why use a clutch fan? maybe because they're cheap? If you're so worried about keeping things cool, a dual setup with staggered temp switching will cure all that temp spiking you're worried about.
If your clutch fan is so awesome, why did you warp your heads from overheating multiple times now? You yourself said you probably didn't have much meat left in the deck surface from all the resurfacing? Doesn't sound like it's working very well. :noworry:
