2160p Stills: Poster or Image Sequence? A Quick But Deep Dive...

So there's long been a question within the SFM community. It's not a particulary common question, nor is it discussed particularly often. And when it is brought up, it rarely stirs any fire. But it is a question, nevertheless: When rendering out still images, is it better to use the Poster function, or render it as a one-frame movie Image Sequence?

I had some time to kill, and I've been meaning to research this topic for a long time anyways. So I finally decided to take a technical look at it. This post won't mean much of anything to anyone who isn't a SFM user. If you're just a casual reader, the May Megapost may be of more interest to you. 

For those of you who are interested in this little technical aside, please, step inside...