A clean engine is a happy engine!

Remember your cylinders are surrounded by the water jacket. The outside wall of the engine is going to be the same temperature as the water. The condition of your radiator, thermostat, and water pump is 10x more important than the cleanliness of the outside of the engine. Keeping the engine cleaned of oil does allow slightly more heat dissipation so it doesn't hurt to keep it clean. But unless your cooling system is maxed out it isn't going to help all at all. IMHO all that high pressure water will corrode electrical connections which is more likely to leave you stranded than an over heated engine. I vote to fix oil leaks then clean, but forget about dust.