With 11+ months to go and very high fees of around £700 each, book the non direct JFK / ATL / BOS etc and you can always cancel for only £35 each. Without doubt there will be some cracking exEU deals for around £1,000 (maybe not MIA but perhaps MCO or TPA) and you can grab one of these. There may even be Xmas fares for around £1,000 cash from London if there's a great deal later in the year