Just match the revvs up and it will be fine, in a manual... Keep in mind, while we're talking about coasting in neutral, believe it or not the car uses MORE fuel to coast downhill in neutral than in gear. Yeah it may slow you down but the fact is it requires fuel to keep the engine idling (coasting), whereas if it's in gear and the engine is spinning faster than 1200rpm, no fuel is injected. Kinda makes sense if you think about it...