Frame size?

I find top tube more critical than seat tube - I'm 5'7" and ok on 54cm square with a shortish stem. Would be happier a bit shorter though. I think I have longish arms but shortish torso for a female.

The classical female proportions are long legs are short torso. You sound pretty conventional!

I share the same short torso/long legs thing but I am a bloke, plus my arms are short. Meaning I need a 50-52cm top tube even at a height of 5' 8". The only bikes Ive ridden that fitted perfect were lo-pro's where the front wheel was 650c. this makes for a very short bike without toe overlap issues.