Based on your comments, you are currently 45 and plan to retire at age 60. Using the life expectancy published by the IRS, your expected life is age 83.
http://personal.fidelity.com/products/retirement/inheritedira/lifeexptable.html
Your 5% might be a little conservative, most people use 7%. If you run the calculations using 7%, retirement at 60, and death at 83 leaving a 0 balance in your 401k would give you a monthly payment of 2341.87 instead of your $2000 / month.
However, if you work until age 65 you would qualify for medicare which you should seriously consider. In addition to the medicare, your 401k also has more time to gain valuable interest which would bump your payment to $3,644.90 / month.
Another way to look at it would be if you rolled it into a 401k now and lived until age 83 and retire at age 60, you still want at least $2000/month. In this case you would need to beat 6.28% on the market. But if you worked until age 65 you would only need to beat 4.68% on the market.
My advice would be to take the lump sum and plan to work until age 65, with the average market return of 7% giving you a $3644.90/month payment while you also qualify for medicare.
Basically taking the lump sum doesn't make sense for people already above ~age 50, but it will vary some depending on your offer.
Note: I am not a financial advisor, but mine told me to take the lump some offer basically because I was younger. I of course was skeptical and ran the math myself.