Thanks for the summary above, this is useful for a lot of people on this thread. As you mention above, it does help to apply for 2 cards on the same day, typically, that comes up as 1 inquiry instead of 2 inquiries, if applying 1 day (or 1 week, 1 month) apart. That may help long term if you plan to apply for other cards, as some banks pay attention to inquires.
Also, there used to be a Citi rule that no more than 6 inquiries are allowed in 6 months (all Citi cards), not sure if that is still in force, but it does help to merge your inquiries together by applying on the same day.
Happy churning.
Cheers,
PedroNY