cbgg,
Great question. I've had several family and friends ask me a similar question, but with less funds (usually talking $10-$50k).
The forum posts so far have been statistically accurate (lump-sum dominates DCA slowdown on average), but keep in mind the studies do not account for market P/E. We are currently near a peak in P/E multiples for the US common stocks.
But anyways, there are a LOT of important questions nobody has asked you:
1) What is your age? Or more importantly, how long do you want to keep this money invested?
2) Are you planning on drawing down immediately on this money, or will it remain fully invested for many years?
3) Related to #2, are you fully financially free of this money, is it just 'extra,' or do you need it for anything in the foreseeable future?
4) What is your risk tolerance? In other words do market fluctuations bother you, or does it not matter as long as you are up in the end? This might sound similar to #2 or #3, but there are many people who just can't stomach watching prices go down regardless of their overall wealth.
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If you aren't drawing down anytime soon and this money is for the long-term (5-10+ years), then imo the advice to diversify into bonds is HORRIBLE. If you are 60-70 and/or trying a 4-5% drawdown type approach, then it's not so bad.
The reason being is bonds are priced based on interest rates and perceived safety (ratings). Interest rates are near all-time lows which means the corresponding bonds, especially long-term, are near all-time highs. If inflation hits us, or if the i/r spikes back up, bond values will come crashing down. Contrary to common belief, it's actually possible to lose 20-30% in a bond fund.
Diversifying your investments doesn't necessarily mean you need/want treasuries or other bonds. Diversifying can include international indexes, emerging markets, growth stocks, value stocks, real estate holdings (REITs), infrastructure MLPs, commodity stocks, etc. Diversifying is GOOD, poor (or "one size fits all") asset allocation is BAD.