I answered 50/50, as that was the closest to the truth. On typical Sunday's, the priests chant 95% in English, but the choir, unfortunately, is probably closer to 50% English--they simply do not know several hymns in English, "Only Begotten Son," "Holy, Holy, Holy," "We praise thee..." and "It is truly meet," are always in Greek, (when the choir sings, September thru June; and because our choir director is nuts (I love her, though), she refuses to chant "Lord have mercy," it's always "Kyrie Elieson," no matter in which language the priest chants. (Our Choir Director claims that because the Roman Catholic Church retained "Kyrie Eleison," in the early first millennium, we should retain it too.) The biggest problem with this mix, is that despite the priests chanting nearly all of the Liturgy in English, it comes across as being largely in Greek due to the choir's obstinance.
I'm sorry, but ...
Priest: Singing the triumphal hymn, crying, proclaiming and saying:
People: Ayios, ayios, ayios Kyrios Savaoth, plyris tou ouranon kai i yis tix dhoxis sou, osanna en tis ypstistis, evloghimenos o erhomenos en onomati Kyriou, osanna en tis ypsistis.
... makes absolutely no sense and benefits nobody.
Anyone who can only speak Greek wouldn't understand a word of the priest's part of the anaphora, and anyone who can only speak English wouldn't understand a word of the people's responses.
Basil, I think you're quite right to be a put off by the choir's attitude, but maybe that's just me.