Stocks: It is difficult to predict future returns, but I would at least calibrate my expected returns based on inflation expectations. Research indicates that equity expected returns and expected inflation move together…

http://www.federalreserve.gov/pubs/feds/1999/199902/199902pap.pdf

…and if expected inflation is lower than average (which I think it is)…

http://www.tradingeconomics.com/united-states/inflation-cpi

http://www.tradingeconomics.com/euro-area/inflation-cpi

…then, all else equal, current expected stock returns should be lower than historical stock returns.

Bonds: I agree with you that the yield to maturity for high quality government bonds is the best estimate for their expected returns, I would just make sure the maturity matches the time horizon. For a 25 year time horizon, I look at bonds that mature in 25 years.

Disclaimer: this is not investment advice.