Guest,Q, you've just sent me running to the cookbooks again. I really haven't got a clue, since I've always been able to use self-raising flour. I didn't know everybody didn't have it. All I can find in reference to this is something I found in the Advanced Commonsense Cookery Book:
"The plainer and cheaper the mixture the more baking powder or cream of tartar and soda is required. Large sponge cakes do not require any baking powder."
I'd go with the middle amount you mentioned, say 3 1/2 tsp/cup and see what happens.
I bet they didn't have self-raising flour on Middle Earth either!
Hollowfox, I just clicked on your link about the book "To Serve Man", because I knew I'd heard of it before in a TV show, and I got my answer - it was an old episode of "The Twilight Zone". I didn't know they had actually produced a book as a result of that show!