A change in viscosity will have na effect. The question is will it reduce flow enough to cause problems. With a low viscocity oil, more oil will flow through a narrow nozzle or oil passage with the same pressure. Sine the oil pump RPM doesn't change and peak oil presure is regulated by a bypass valve, you will probably see a drop in the volume of oil flow at higher RPM's. At high RPM's it may not be a question of lubrication, but rather one of cooling. Oil it used almost as much for cooling as it is for lubrication. That's why there is an oil cooler integrated into the engines cooling system. At lower RPM's, the high viscocity oil will rpobably increase drag on the engine as the crank will need more energy to move through the oil in the bottom of the crankcase. The oil pump will also need more energy to pump a thicker oil.

Bottom line. A heavier weight oil probably does protect better in many cases, but unless the engine is designed for it's use, you might do more harm than good.