Many interesting points here.

The mental arithmatic is usual for someone like me because I have limited experience in sight reading and first try to figure out what key I'm in ("gold dollars are ever bright" or "fat boys eat apple dumplings"). Then I can change to the new key and remember which notes are sharp or flat in that scale. The issue came up because I was in a trio, and we all needed to instantly transpose to the same key.

(Dermod, according to "gold dollars...", five sharps would be B, no?)

I don't understand the F#, comments. What's the comma?

As for key and mood, I definitely notice a different mood in some keys and remember a thread way back on the subject where many of us went into great detail on the subject.