Thank you; I finally found the 'Breve' or 'Double Whole Note' on Sibelius, so I edited the score to reflect this. :)

Thanks; I guess I'm more familiar with F-sharp Major than G-flat Major. Why not F? I guess because I just like the sound of the key better and my choir doesn't tend to keep things in F-Major as in tune as they do when it's a half-step up. :)

That's really interesting about the harp, however. I have never really written anything for the harp nor have I ever really needed to. (I doubt a harp could get up our winding choir loft staircase)!

An awesome reflection. I've come to see F# with a certain heroism. It's brightness never seems to fail; my choir's intonation is much better in that key and, like I said earlier, I just like how it sounds. In comparison, F just feels wooly and thick to me (hard to describe). And I avoid a capella music written in G like the plague. It NEVER stays in tune for us and ends up reverting down to F# anyway, which is another reason I probably defer to it. :)

The key signature of "A Hymn for St Cecilia" has 6 flats (rather than 6 sharps), in deference to the concert harp part. I cannot imagine how a harpist, playing in 6 sharps, could handle a transient A-sharp major chord, whereas playing in 6 flats makes a B-flat major chord a rather easy change of just one pedal.

As for flat keys versus sharp keys: Yes, A major is brighter than A-flat major (and entails one fewer accidental). Similarly, E Major is brighter than E-flat major - but then F major is (to me) brighter than E major. Oh, while I've heard that some choirs cannot seem to tune F major (and usually drift flat), I find that such choirs tend to drift flat in other keys, especially G and A-flat major - but surprisingly, F minor (with 4 flats!) stays in tune rather well, or at least fares no worse than E minor - although I tend to prefer E minor to F minor.

You can judge for yourselves whether "A Hymn for St Cecilia" lacks "brightness" or even "saintliness" with 6 flats in the key signature (the tonality gravitates between D-flat & G-flat major):
    PDF score (letter size).
    MP3 sound file (112kbps).

A415 (or thereabouts) is a common tuning for harpsichords & string instruments playing early music, not much a problem for brass instruments (especially sackbuts, but also valveless horns and trumpets), but more of a problem for non-baroque woodwind instruments (which must otherwise transpose, if possible). For absolute (perfect) pitch singers, it is often also an aggravation.

'Perfect pitch' is, in western music, perfect recall of all notes tuned relative to A 440. Identifying notes that haven't an A=440 basis would be a species of 'relative pitch', whereby pitches are identified relative to other, known ones.

Perfect Pitch is sometimes called Absolute Pitch, both of which refer to perfect and absolute recall of every pitch in a gamut which has A=440 as its basis..

Relative pitch differs from Absolute or Perfect pitch in that notes are identified only by judging their distance from one known pitch.

From the standpoint of physics, designating a thing we call A at a conventionally agreed number of VPMs is purely arbitrary, a non-existent, purely conventional category with no objective reality or ontological existence. A, regardless of agreed upon VPMs, is a made up thing, it is what we have decided it is. It is not a thing in itself, and has no objective realityl

These matters apply only to music of our diatonic Western musical heritage. Other cultures display many different systems. (And their attempts at composition using Western idioms most often result in very poor music.)