I am still a beginner so I am not qualified to give you advice, but this articles might give you more guidance...
http://jlcollinsnh.com/2013/12/05/stocks-part-xx-early-retirement-withdrawal-strategies-and-roth-conversion-ladders-from-a-mad-fientist/My understanding is that only traditional IRAs can be converted to Roth IRAs, and that is one reason besides fund costs that might encourage you to switch over to a traditional IRA. People who are receiving all of their income at low capital gain rates can potentially convert traditional IRAs to Roth IRAs tax free. Based on my elementary understanding the amount that you can convert tax free depends on your total available exemptions/standard deductions and whether or not you are still in the zero tax bracket. If you successfully convert a traditional IRA to a Roth IRA you are paying no income tax on both your original investment and your later withdrawal(from the Roth).
Look at the 2015 tax brackets to see how you can potentially qualify for tax free conversions:
http://www.forbes.com/sites/kellyphillipserb/2014/09/17/2015-tax-rates-brackets-exemption-amounts-may-save-taxpayers-money/Right now capital gains and qualified dividends are taxed at zero percent if a taxpayer(s) are in the 15% ordinary income bracket. For example a married couple in the 15% ordinary income bracket(up to $74,900) could live on $54,300 of qualified dividends and capital gains and then roll over up to $20,600 of their traditional IRA to the Roth IRA tax free. This couple in this scenario would pay zero income tax in 2015, while converting $20,600 of the traditional IRA to an account that won't be taxed at a later withdrawal date.
The rollover from the traditional IRA to the Roth IRA is technically a taxable event, however $20,600 of ordinary income can be offset by the $8,000 in exemptions and the $12,600 standard deduction for a married couple. If the married couple is itemizing deductions then they could still roll over $8,000 tax free by just using their exemptions. You can also use your children's exemptions as well for this purpose.
What I haven't figured out yet is if standard deductions and exemptions are first applied to ordinary income or capital gains income. If exemptions and standard deductions are first applied to ordinary income(or the roth conversion) than a person can theoretically still take advantage of paying a lower effective tax rate on Roth conversions while leaving the 15 percent ordinary income bracket. If standard deduction/exemptions are applied to capital gains first then the Roth conversion would be taxed at a minimum of 25% when leaving the ordinary income 15% bracket.
Disclaimer: I came across the concept of Roth conversion recently and part of my intent in writing this post is to see if my understanding is correct and allow people to correct any holes in my understanding. That being said I believe the Roth conversion concept is what you were referring to in your original post.