Mike,
I'd take the St Cyr trip with the club and then go the Eurostar route with the missus. Sounds very romantic but if you're low hours and she hasn't been on any long trips before it could get very stressful and her ideas of romantic and yours won't coincide. Take here on some smaller trips first and build up to a longer one. Like being low and slow, an early negative experience with a Significant Other is very difficult to recover from.
Unless BOTH of you are signed up to treating the aircraft journey as part of the "romantic experience" I'd avoid it - trust me!