If you are planning to power up everything you get, you will do marginally better by setting posts to 100% power up.
When hbd is below a dollar you will get fractionally more hive because the chain always pays 1usd of hive.
When hbd is over a dollar then going back to 50/50 is the maximizing play.

Converting hive to hbd comes with a 5% tax that is burned.
Hbd to hive is friction free.
Better to buy hbd on the internal market to miss out on that 5% fee.