Another point to ponder... Water to oil cooling transfers far more heat, far quicker than air to oil. An air to oil cooler must have a much larger area to provide the same cooling.
I agree. As long as your cooling system is in good working condition, adding an oil cooler has little or no effect on the coolant temp. The Ford diesels we work on have oil coolers of the same stacked plate design in the belly of the engine and lowers the oil temp by at least 25-40 degrees F. The Cobras use them, all the diesels since the 94 DI (ford) use them, Police cars use them, just about anything with a towing package uses them... etc. If they didn't work, they wouldn't spend the money to up-fit them.
Ratio411- can I see a picture of your hose routing? I happen to have an 351w with the cooler and lower hose. If it fits well I may as well use it.