Bob Kauflin is always right on the money. Here he says just about everything you'd need to know about finding the right key to pitch songs in.
There’s a wide variety of opinions when it comes to what’s an “appropriate” key for congregational singing. My basic approach is to keep songs from a low A to a high D, but there are certainly exceptions and other aspects to consider. The strongest range for the congregation seems to be between G and D.
other considerations he looks at are;
Can you hear the men straining? Or the women dropping down to the men's range?
People often need to sing fast songs at the upper end of their range in order to 'belt it out'. Slow and low works fine.
Range is important but there's a big difference between a song hitting a D once in the chorus and one hitting it 6 or 7 times.
If you use the option of modulation in hymns or hymn-like songs the final verse or two can be a little 'too high' as the people will only sing the top notes a couple of time rather than getting fatigued over 5 minutes.
"If your church naturally sings in four parts, it’s possible for the melody to go up to an E or F without a problem, because the guys who can’t hit those notes will generally be singing the bass part".
Bob's conclusion is that we ought to primarily serve the Church and sing songs in keys that are comfortable for the congregation, not just the leader. If you're more comfortable in a higher range add harmony or vocal fills.
Read the rest - Finding The right key to sing in.