Ok, so I've been going through the numbers. Of course I have to make a lot of assumptions:
- No state tax, 24% tax bracket during your career, 22% in retirement, 15% capital gains tax rate
- 5% interest in the MBCBP, 8% return on your own investments
- Buy an annuity with the MBCBP total, returned at 6% per year
- Distributions on your own investments at 4%
With those assumptions and more, it will take 28 years for your own investments to provide more income than the MBCBP. At a 9% return, 22 years. Those numbers stretch are 31 and 24 years respectively with a 5% state income tax.
So I guess if your retirement horizon is more than 30 years out, then it's in your best interest to not have the MBCBP. If it's sooner than that, the MBCCBP is the better option.
Depending on your age and previous savings I would not agree that the 401k isn't adequate, but that is a larger discussion.
I guess I shouldn't say "adequate". Fully tax advantaged, maybe.