GP was talking about saving $1200 out of $3400 take-home, which means living expenses are $2200/mo, or $26,400/year.

Let's leave things in "today's dollar" terms for simplicity: A 4% annual withdrawal from $1.4M would be $56,000, or a big upgrade over $26,4000.

A 4% annual withdrawal from $4M is $160k. But as you say, it's the equivalent of $56k today.