If this weren't already complicated enough, another variable I think you need to consider is your expected tax burden post-retirement. If your spending is sufficiently low, your post-retirement tax burden should easily be 0—making 401k contributions really valuable, as they're completely avoiding taxation. Remember, your 401k contributions avoid taxation at your *top marginal tax rate*. E.g., if you're in the 22% tax bracket, maxing out your 401k saves you $4,290 in federal taxes + whatever state/local taxes you owe. So depending on your circumstance, this could be a much better deal than your 15% discounted GESOP. Especially once you consider short term capital gains taxes you'd have to pay following your strategy of selling asap.