I know it varies by speed, itinerary and weather. (The further between ports the faster they need to go.) We were on Deck 8 forward (8002, you can't get any more forward on that deck), but we didn't feel any motion on our sailing. Not even in Palo, or the MDRs aft, which usually has some vibration from the engines. That was probably the smoothest sailing we've ever been on.
The seas weren't particularly calm and there were waterspouts and heavy sustained winds as one point, but we hardly felt a thing.