You must mean PRE TAX 401K conversions ... and you usually cannot convert from a 401K to a Roth 401K (ask your employer) ... so do you mean you will convert to a ROTH IRA ?
And yes, the converted amount will be taxable in the year of conversion so the timing of how much and when could make a difference. You may wish to discuss this with a financial planner or a tax preparer to figure out the options.
