I used the same formulae as you did along with this chart published by Evolvent Design. There is a short video from them also that gave me more confidence in deciding it was M1.25 ( I know you hate YouTube vids but it may help someone else.) I decided on a 20 degree pressure angle because I couldn't find any information about any other angles being used for M1.25 gear teeth. I went through the selection for M1.25 gears from Maedler North America (these guys sell all kinds of cool stuff) and there is no mention of any angle other than 20 degrees.
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