As we seem to be in agreement that the 401k and IRA are "old person" money. The question at hand is to determine HOW much is enough to invest in your 401k and IRA.
SCENARIO #1:
If you're 25 now, and you put 23.5k in your 401k/IRA every year for 10 years at 7% growth, you'd have $347k in the accounts by the age of 35. If you stopped investing in your 401k/IRA at age 35, by the time you hit 57.5, you'd have $1.88million in those investments, not included Social Security.
Meanwhile with $15.5k invested annually in your other accounts, you've amassed $229k in your short term accounts. Or roughly 7.5 years expenses.
Obviously 1.88m in your old person account is too much. You've invested too long into your 401k and IRA accounts.
So, SCENARIO #2: A more short term Example.
You only invest in the 401k/IRA at $23.5k for 4 years, and your investments reach $111k. You stop investing in your 401k/IRA at age 29 and by the age of 57.5, the investment reaches $844k. A safe withdrawal of 4% is $33,760. You've secured your old person fund in 4 short years or working. Compounding interest does the rest.
Meanwhile you've invested $15.5k for 4 years, and 39k for the following 6 years. After ten years of investment in your "young person" investments, you've amassed $410k. 13 years of expenses, and your 35yrs old.
Option #1: At this point, with a return of 7%, you could begin withdrawing $32,880 from your young person investments, each year until age 58, when your 401k and IRA become available. You're young person investment balance would drop each year, but you'd run out just in time for old age retirement to kick in. RISKY
Option #2: You now find yourself with an income stream of 16k annually, and expenses of 31k. You only have to earn $15k a year to maintain your current standard of living in your part time retirement. And your investment balance would remain stable. Of course, with a current annual net income of $70k, this represents only 2.5 months of full time work. Or 400hrs of work. Or 8 hours of work a week. 1.6 hours a day... Annually. And when you hit 59.5, you'll never have to work again. Less RISKY
Option #3: You stop working full time at 35, and work 5 years longer at part time instead. You now net $35k instead of $70k. Enough to cover your full annual expenses while letting your young person 'stache' continue compounding. 5 years later and your young person stache grows from 405k to 568k. Essentially 20 years of expenses if you cut back a bit, and you retire. You're now 40 and 20 years later your 58. At which point you start withdrawing from your 401k/IRA. LEAST RISKY. You'd have to forgo earning any money (hard to believe).
That represents 10 years of full time work and 5 years of part time work to bring yourself to full retirement. And you'll be rich!
Of course, you're a single individual. MMM was working for many years from with the Dual Income No Kids arena, often times contributing over $100k annually into his investments, not including his compound growth. His joint income near the end of his career approached $200k. All while sharing expenses with his wife. You're along in your boat and you have to power the oars yourself. It's a longer battle.
Also, this assumes your earnings don't ever increase, you never marry, you never have children, your savings don't increase, inflation is nullified, and your investment returns remain stable. You could easily earn more in the future, meet a partner, etc and be further along than anticipated, or invest poorly and have to work longer.
The main thing is to find the break even point with your investment portfolios so as to ensure the earliest possible comfortable retirement date.