I am genuinely confused by London salary in dollars. That makes absolutely no sense.
$100k in SF = $70k in London = £55k in London - is that what you're saying? In that case, we both agree, the costs of living are a lot cheaper (so are the salaries).
Google top salary is 85k base for senior developers, which is shit (numbers from the guys I know, some of which are openly mocking Google and advising people to never go there because of the pay).
Not sure about the other big 4 (Facebook/Microsoft/AMZ), not much more allegedly.
Quants make a shitload more than developers. The standard in finance institutions is £130k base + variable bonus. (Well, now that I think about it, the difference might be the industry, not the role :D)
As for what the top developers make in the top few financials institutions. I need to get a few guys drunk to get accurate numbers. But I already know that it is definitely higher than at Google.
What's your numbers for top performers in NY and SF? In London, there is no money in the usual valley companies. That's just how it is.