Years ago, I played at a funeral at an RC church with a west end organ, miles away from anybody; can't remember what the first hymn was, but the second was 'How Great Thou Art'. The priest managed to announce them in the wrong order with 'How Great Thou Art' first, so, rather than fumble through the hymn book, I decided to busk it and a quick mental run-through of the first line or so pointed me to the key of F. That all worked fine until the second half of the tune where the hapless congregation suddenly found themselves having to screech up to high A's. I've always been wary of that hymn ever since (as I'm sure they have)!