You can pay the tax bill separately, which is a better move than letting it come out of the rollover amount if you have cash to afford it.

I still don't understand why you'd convert to Roth.

My tax rate will be higher while I'm working and earning a salary than they will when I'm retired.

Also, by keeping the base amount higher (pre tax), won't I have more growth than compared to the after-tax amount?

It'll be more absolute dollar value of growth, but wouldn't be higher in percentage, and taxes are going to come out as some percentage of any money that was put in pre-tax at the time you withdraw.

If you didn't work the entire year or your income was otherwise variable (bonuses or whatever other reason) then it makes more sense than usual to do roth contributions, or rollovers/recharacterization from traditional to roth, in lower-income years. Assuming you can afford to, and want to maximize what you put into tax-advantaged accounts.

The annual contribution limits are also on dollar amount that goes into the account, so if you're maxing out then you can get more out of a roth ira/401k overall. Not all companies offer the choice of roth on their 401k plans, which is a little annoying.

One reason for Roth would be if you think tax rates will be higher when you retire.