The math does not work out for that.

Let's say you make $100,000 per year. Saving 80% would mean saving $80,000 per year, and living on $20,000 per year. After 5 years you would have saved $400,000. 3% of $400,000 is $12,000, which is only about half of what you need to equal what you'd lived on for the past 5 years. You'd need a 5% return in order to make $20,000 per year from $400,000.

And this doesn't even take taxes in to account. Good luck saving 80% of your net when taxes alone eat away more than 20% of your net. You're also going to wind up paying taxes on the 5% return, effectively requiring maybe a 6% return (or probably significantly more, considering how much you lost in income taxes in the first place).