650-900gbp per day sounds similar to southern Sweden. Hourly rates here go between 750 to 1300 sek.
650gbp x (365 per year - 30 vacation days) = 217750 gbp
Isn't that already very high? in comparison to some US salary?
For a fair comparison vs a full time job in the U.K. when I compared the two recently, I was using 226 working days per year (261 week days - 8 bank holidays - 27 paid holiday days). Of course if you don’t want to take so much holiday or want to and can work weekends then you’ll earn more!
650 x 226 is £144,460 for the record, still nothing to complain about!
Working as a consult comes with its own risks (not much worker rights, very little or no notice period when terminated etc). But those risks are not too bad when you consider how little worker rights one has in US.
I'm pretty happy with the trade-off w.r.t. freedom of association where a business can fire me for ~any reason at any moment, and likewise I can go and get a new job paying mind-bogglingly huge amounts of money with minimal friction. (No amount of "worker rights" will save you if the company employing you goes under, like so many did in the dot com era.)
That being said, I don't know if I would plan my life entirely around being in the absolute top %10 of engineers. Avg. seems like a better figure to compare when speaking of whole markets/countries.
I plan to be at top %40 of engineers in a given field as a specialist and be a generalist overall. Seems like EU is a better fit for me then.
40th percentile compensation in the US is probably still much higher than in the EU, but you do you.