At least historically, the research I've seen is that one is better off keeping risk in the equity side of a portfolio, not trying to eek out gains on the fixed income side. So that would suggest sticking with intermediate duration, government bond (funds).

You're not expecting it to earn much, but it should hold its value over the long term. This will reduce the expected return of the portfolio, but the goal is to get volatility to a level you can stomach, allowing you to ride out fluctuations on the equity side. Because even though we can all look at the current situation and say the stock market appears overvalued, we can't know how much higher it will go, when we've hit the top, or once it starts declining, when we've hit the bottom. Even experts do no better than luck would dictate at that game.