The bad thing in Berlin is that 60-70K is really a ceiling, if you want to stay in non-managerial engineering, and that amount is not something unrealistic for engineers living in cheaper parts of the world working remotely, so there is not much incentive to move to Berlin.

Btw, why do you find London much expensive? I mean, you can rent (or mortgage) a decent apartment in the nice district for ~600 GBP per month. And the food, goods, appliances, etc... is similar, or cheaper. And most importantly - people speak English! :) The language factor was a revelation for me, after spending some time on the mainland Europe.