The 80 movement per hour cap applies, regardless of the runways in use. It can't be hit on a single runway (mid 50's is a rough max). No idea where the 20kts comes from, ICAO maybe? utilizing both 34/16 and 25 for arrivals and departures doesn't really increase any movements, it would likely do the opposite as complexity increases. A 25kt limitation would likely eliminate a high % (80 at a guess) of 25 only days. 30kts would almost eliminate it altogether. Whether that's considered safe and would get signed off is another question.