You'll also want to consider possible side effects due to the increase in AGI. It might make you subject to Net Investment Income Tax. It might reduce your itemized deduction for medical expenses. There are a number of other possibilities, so you'll want to prepare simulated tax returns with and without various amounts of Roth conversion to calculate the actual marginal tax rate. The increase in AGI could also cause increased Medicare Part B and D payments (if you participate) of about $4,800 for the year two years after the year of the conversion.
Don't forget to consider state income taxes.