This is a good key for instruments, but high for most singers. We've been staring on the D below this. Whatever key you end up in, the descant starts on the last note of the melody, so those who know the harmony can get their pitch from the lead singers. We've found that any more than about 10% of the singers on the descant is too many. If you have fewer than ten singers, have only one descant; in a roomful, three or four has been plenty, if they can sing it clearly, because it's high enough to carry, and you don't want to overpower the melody.

If you want to sing along with the post-battle scene in Henry V, the words used there are:

Non nobis Domine, Domine, non nobis Domine,
Sed nomine, sed nomine to da gloria.