I can't remember how it was exactly, but I can tell you that I studied the history of the English language, and I think that words such as steak, break and great have an [ei] diphthong instead of an [i:] because they stem from the Middle English upper-class pronunciation. The spelling ea corresponded with a long, open [e] in the Middle Ages, whereas ee corresponded with [e:]. The first evolved towards present-day [ei], and the second towards present-day [i:]. However, in the lower class the long, open [e] evolved first to [e:] and then to [i:]. Nowadays, the pronunciation for ea is that from the lower class in the Middle Ages, that is, the upper-class pronunciation that should be used for ea was lost in time, except for those three words. I'm not sure about this because it is a long time since I studied this. Saludos desde España.