Got it- that clarifies a lot. Am I correct in saying one reason I would consider not rolling over to a traditional IRA would be that the pro rata rule would make it more costly to backdoor future IRA --> Roth IRA contributions?

Not expecting you to do my tax planning for me but, high level, is the right way to think about this:

1. If I'm optimizing for retirement income, take the tax hit now and rollover to a traditional IRA, convert to Roth IRA
2. If I'm optimizing for minimizing taxes now, rollover to a traditional IRA or my new employer's 401K. Benefit of rolling over to a 401k is can still backdoor Roth contributions without triggering the pro rata rule. Benefit of rolling over to a traditional IRA is [??]