How to think about equity refreshers / annual stock grants?

[L M]

I have an offer from Google and several "startups" (worth over $1B currently, likely to IPO in the next few years). My Google recruiter said that equity refreshers (which Google offers, but the other startups do not) can be a significant chunk of your pay, but he said he didn't know firsthand what kinds of numbers to expect.

So how should I be evaluating equity refreshers? The problem is I don't know what to expect from Google in terms of annual stock grants. What is the range here? What can you expect if you're in the top 10% of performers? I've heard that you can receive 2x of your initial stock grant every year, vesting over 4 years, but I don't know if this is true of engineers at the bottom of the ladder, even if you perform extraordinarily well.