Chip, specifications for Oceania ships are 18 knots. Specifications for the Diamond are 12.5 knots. Specifications for the Mariner, Voyager, and Navigator are 20 knots.
Doug, Oceania ships are not entirely non-smoking ships. However, there are only two areas where passengers can smoke. First, there is an area in the Horizon's lounge, and second there is an area on the Pool Deck. Passengers are not permitted to smoke in their staterooms or on their verandas or in any public areas except for the two designated areas listed above.
Bob and Frances, you are correct. All three Oceania ships are former Renaissance ships and are identical. The first two ships were refurbished in the past two years. The third ship is currently being refurbished and will begin in Asia in November of this year.
Oceania may not be for everyone because they do not offer any 7 day cruises. Most cruises are 10-14 days with some longer.
According to their Director of Sales when schedules are first released they offer 2 for 1 discounts and free air for a limited time. After the initial offering the prices and cost of air rise based on demand.
Hope this helps answer some of the questions.