Wage-COL trade-offs across Europe

I've been investing a lot of time recently into seeing where the pocketable difference is the highest. A lot of European asset managers and bulge brackets have offices all over Europe, incl. Frankfurt, Paris, London, Zürich, Milan, Madrid - you get the idea.

The thing I have been trying to figure out is where can we expect the opportunity to be the best? I got a fairly general approach so far (on a couple dozen hours of research):

FFM - servicable rent, low-ish COL, high wages

Milan - low rent, low COL, medium-to-high wages

Zürich - medium-to-high rent, medium-to-high COL, high wages

Paris - low-to-medium rent, medium COL, medium-to-high wages

Madrid - low rent, low COL, low-to-medium wages

LDN - high rent, high COL, high-ish wages

A lot of people talk about the need for a recognized employer, but if you work for an MNE (multinational enterprise) that has offices everywhere, you could still eventually get a "lateral" to a country with slightly better wages. 

Anybody have some other ideas based on what I should be analysing which city to go to? Keep in mind I'm not originally from any of these countries.