Generally speaking, you need to save an amount equal to your current income/.04.

If you make $80k per year, divide this by 4% (.04), the result comes out to $2 M.

This $2 M could come from many places

1) SS
2) 401k
3) IRA (Roth preferred)
4) taxable accounts
5) downsizing house to a condo (might create ~150k-200k)

SS:
Of the 80k per year needed, SS might generate around 24k of this. More than likely the SS income would be taxed. (80k is a "significant" income and depending on age, it could be assumed anyone with a significant income in retirement will be subject to SS payments getting taxed).

401k. 401k withdraws will be taxed. 80k is currently in thr 25% tax bracket. meaning tax paid is $8735 (tax owed in 10% and 15% tax brackets, up to $63,000)+ 80,000-63,000=17000*25% is $4250. Federal tax owed each year would be $9285 (there is now 71k you have to pay state taxes and other expenses with).

Roth IRA withdraws are "tax free". If you withdraw 80k from a Roth, you owe no taxes on it. This is why a Roth is the prefferred mechanism for funding retirement, IMO.

Taxable accounts. If you withdraw 80k from a taxable account, you will only owe taxes on the gain (when you sell). If you purchased a security for 20k and sold it for 80k, you have a "capital gain" of 60k. 60k would be taxed at 15% which is $9000 (this is less tax than you paid on same 80k withdrawn from 401k). The 60k gain assumed here is conservative (most gains would be much less than 60k).

So the question remains- which account should you use to fund retirement?

I suggest all types. Contribute to a 401k. It will lower your current tax bill. Because SS still exists, invest the 401k aggressively. Worst case is you collect SS and treat SS like a bond/cash/ annuity type instrument if aggressive investing fails.

A Roth account is the "denser" than any other account. it costs more to put money in a Roth today (because the money going in is taxed before going in). But the tax free withdraws coming out are a key component to retirement income planning.

Taxable accounts. If you become ineligible for a Roth contribution (income greater than 150k for married couples, I believe), then use taxable accounts to allow for cheaper capital gains tax rates in retirement. Taxable accounts should consider using individual stocks as opposed to mutual funds (to avoid intermediate capital gains taxes while accumulating assetts).

Downsize the house if it makes sense. This might reduce the 80k income needed to 75k (lower utilities, property taxes) and create an extra 150k or so you could invest in a taxable account.