I have a slightly different take on this. I believe that the question of whether or not to convert should be principaly based on one thing: have you or have you not reached your financial target (ie. the amount you think you'll need last for the rest of your retirement)?
If you haven't reached the goal yet, then it's in your interest to keep the leverage of what you would otherwise lose in taxes so you reach your goal sooner.
If you've already reached your goal, then convert as aggressively as you can (without of course dropping below the goal amount due to taxes).
