Six percent annually.
That said, it is a fantasy, unless you intend on your retirement getting cut short by death prior to you exhausting your money. The standard recommendation for someone who is much older (i.e. can rely on death to moot insolvency with greater probability) is that the safe withdraw rate is 4%.
With a withdraw rate of 4% and a standard mix of stocks and bonds you can be fairly confident that, assuming the future looks something like the past, you will not run out of money within your lifetime. (Most people will in fact see their money "go infinite", i.e. their portfolio expands faster than their withdraw rate and when they eventually pass away their heirs and government get to toast their name quite a bit. However, the prudent investor doesn't plan on being "most people", they plan on being the unlucky sod who bought at the top and sold at the bottom.)
Some of the applications sound a lot more like a careers break, vacation, or a few years off to volunteer.
Naturally, you'd need to consider how much you need, what are acceptable risk & such depending on your application.
His high low estimates for how much you need also vary almost 7/1.
I think it is most prudent for non-investing professionals who want to live this life to buy two annuities, one denominated in the currency of their home country and the other denominated in the currency of their new country.
http://finance.yahoo.com/q?s=tlt
...that's as safe you'll get.
Insured munis at 5
http://finance.yahoo.com/q?s=pza
Emerging at 6
http://finance.yahoo.com/q?s=emb
Junk at 13
http://finance.yahoo.com/q?s=jnk
Mix and match.
For 3% inflation, you need 7% nominal returns to make 4%. You're already into pretty risky territory there.
Also a 60 - 40 stock/bond is actually safer than a pure bond portfolio because of inflationary risks and has a higher expected return over 10+ years. The only real trick is to avoid single investments, be they a stock or an industry.
That's currently a slight stretch given interest rates in most OECD nations, but definitely achievable without effort over a longer term (eg, 6% pa for 10 years).