So if you did postpone taking FERS, even for 3-4 years, could you move even more into your Roth and/or draw living expenses off your tax deferred up to the 15% marginal tax rate? This would allow you to maximize the capital gains (pay 0% tax) and grow your FERS at 5% per year.
I'll be grappling with a similar decision when I turn 57 or 58. I'm still thinking through all my options.
I think the answer is "no"! Why, because I don't think you can contribute to a Roth if you are not working? I may need to discuss with a tax investment professional next year.