One consideration that offsets that is medical insurance. If your health care is not fully covered by your employer.
I ran some numbers once and the "rent difference" was roughly $3k (typical 1 - 2 bedroom apartment at $4k vs. The roughly $1k I spend) and the platinum medical looking like roughly $500/mo
Add in a car, ($0 in Toronto, $1000 in The bay w/ parking, insurance, gas & the vehicle)
All said and done, $55k appears to make the cost of living difference "break-even"
If I'm on roughly $100k in Toronto, $155k would be even. Now that doesn't adjust for exchange rate, so you might get ~20% play there. Maybe the $135k median I've read about is roughly on target in terms of total food cost, etc...)
I think there'd be some cachet to having a "big five" employer on your resume, so a year or two in one of the mega-shops would add value to future earnings if you started looking elsewhere, or a handful of other unicorn-class names might have a similar impact.
All in all, I'm not convinced that taking a San Fran gig would necessarily feel like streets paved with gold and scooping up baskets of money (which grows on trees), so much as it'd be a nice, sunny, ultra-nerdy town in the heart of movin' & shakin'
Incidentally, if anyone would like to disabuse me of any errors in my napkin math, I would welcome it. I'd love to get a more realistic idea of the difference.