I have the Barclaycard Arrival Plus and definitely wouldn't recommend it for you since it is a fixed amount back (2.22%) and you will get far more bang for your buck using a mileage transfer program - whether it is Chase UR, Starwood SPG, or Amex MRs.

Also, doesn't the Amex Platinum which you already have give you a free companion ticket when you book 1st or business class international? I don't know this for a fact but I'm pretty sure I read about this at some point.