Last year I was in a similar boat, but wanting to get from MIA to London. I checked online about every day for deals for our June trip. Finally, in February, there was a one-day sale (on Travelocity), and we got non-stop Virgin tickets for $488 including tax. However, if that one-day sale hadn't happened, we saw some for around $650 later. It depends on your level of risk-aversion - do you want to wait around for a great fare, and miss the not-so-great, ending up with the terrible?