Award levels from US/Canada largely correlate with revenue fares these days. So you can use Google Flights in Map View mode to find destinations with cheaper fares and that will mostly correspond to having lower award levels. There's some decent roundtrip awards to LHR right now (ranging from 40.8K roundtrip in coach to 153K roundtrip in D1 with Amex discount) from many US cities. But unfortunately they are only valid for trave through early May.