Imho, sell just enough every year, to convert and fully fund your Roth IRA contribution amount; for that year.
Then within the Roth, set up an automatic purchase of the total stock market index fund; dollar cost average the purchase of the index fund, on a weekly basis.
I did the above for years while at Cisco (I sold my RSUs, each year, to fund the Roth). That money is now a good chunk of change and am very thankful for my time there. I felt it was better to pay a small amount of taxes each year in selling the RSUs, and then both never have to worry about the taxes on a big chunk of RSU; plus then convert to an index fund to get away from being invested into one stock.