The expression As slow as a turtle recently appeared in one post. I think this must be an AE expression (if it is genuine), since turtles (in the sea) can travel at 20 mph and tortoises (land creatures in the UK) cannot walk faster than 1 mph. According to Merriam Webster only tortoise refers to a slow person, not turtle. So to say "this computer is as slow as a turtle" would seem to be a strange expression, which I have never heard in the UK. Are speakers of AE familiar with the expression?