Conjecture? Subtle results? Temp readings at different points of the head, while at steady state on an engine dyno issounds like a good procedure to me, with very conclusive results to boot! Heat Transfer is not voodoo. The back of the head is hotter because it receives the hottest coolant and the least amount of flow. You improve cooling by either increasing flow, delivering cooler coolant, or both. Exactly how much more evidence do you need? I've been saying all along that running it to the radiator would be a better solution to plugging (with a properly restricted line) and much better than looping. The evidence very strongly points to it. What got me thinking originally was John Coffey's post about how he's routed the heater supply to the thermostat housing. While that may be effective (I don't know), I concluded that routing it past the thermostat was a better idea, since you'd be in more control over where this coolant is flowing. If instrumented testing proves me wrong, I'll happily eat my words.