You may find this minimum required distribution (MRD) calculator a useful tool in answering your question:

http://personal.fidelity.com/retirement/retired/assets/mrdframe.shtml

Here were some of the things that I learned.

The MRD climbs pretty steeply. You may find that you are required to withdraw (and pay taxes on) far more money than you need for expenses. In fact, you may find yourself in a top dollar tax bracket.

Also, consider the tax consequences on your heirs of inheriting any undistributed TIRA assets.

1) Before 2010, your married, filing jointly, AGI (calculated before any Roth conversion and/or MRD)needs to be <$100,000 to do the conversion.

2) You can convert any portion of your TIRA assets, spreading the conversion over several years, so that the tax bite is kept <25%, for example.

3) This gets increasingly hard to do as your MRD climbs. In your case, you have some 'wiggle room' given your 5 year age difference.

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