This is why you should reduce a 100 - 125k salary by 40k through salary sacrifice, paying into a self directed pension. Taxable income is reduced to £60 - 85k.
> Also, VAT there is much higher than sales tax in CA.
Yes but there are no property taxes in the UK, which I'm sure far outweighs the difference in sales tax on a yearly basis. Also VAT isn't applied to everything, it is reduced to 5% for fuel and 0% for food. I'm making the assumption I can cash purchase a home I actually want to live in in the UK. Purchasing a house isn't really optimizing net worth either, but it is a stability factor I would rather have. I'm looking at $1.8m-2m minimum in SF for a property I would actually want to purchase and live in. I'm sure there are plenty of massive homes in the middle of nowhere I could purchase but am I going to have a job I want and live near interesting like-minded people? Probably not.
> an acquaintance of mine had to pay ~75% marginal tax on AMZN RSUs
RSUs are not a qualifying option in the UK. Most startups in the UK are offering EMI share options, which are more tax efficient than any offering in the US unless you look at early exercising with an 83b election, which is obviously significantly riskier.
> The savings from your ISA accounts will be negligible until your portfolio grows
Yes that's the point, if you grow an ISA to 1mil in value over 25 years, drawing down that ISA at a 3% rate is a significant tax-free lump sum contribution to your yearly income.
I won't go into the full detail but I reckon that with the combination of an ISA, pension allowances, and dividend/capital gains allowances on private investments, you can draw nearly 97.5k in income and pay only 3750 in tax, and there is no AMT in the UK.