Interestingly optimistic. I've been doing my recent retirement calculations with 5% nominal returns. I suppose it's because I'd rather be pleasantly surprised in retirement than starve.
30 year treasury bonds are currently yielding around 2.6%. Doesn't that mean that investors are pricing in a significant risk that they won't get a better return on other investments over the next 30 years? The world might be following Japan's lead here.
5% nominal returns, then ~2% inflation and income taxes on withdrawal. That's going to require a high savings rate.