I don't think there's anything wrong with the original logo, except of course that it doesn't represent London. Other Rails Girls groups do their own, so it seems like an acceptable thing for us to do our own.
Regarding readability, the logo is not intended to be read at that size. It has quite strong iconography, which makes it recognisable both as something representing Rails Girls and London.
Does anyone else have an opinion on the new logo that they have not yet voiced (and would like considered)?