[acdha]

Those are what I would assume for performance when the system is stable. The concerns come from bursty behaviour — for example, if you put something new into production you might have a period of time while S3 is adjusting behind the scenes where you'll get transient errors from some operations before it stabilizes (these have almost always been resolved by retry in my experience). This is reportedly something your AWS TAM can help with if you know in advance that you're going to need to handle a ton of traffic and have an idea of what the prefix distribution will be like — apparently the S3 support team can optimize the partitioning for you in preparation.