I think your figures are per eye, So your totals should be doubled. The 3.7Mpix (2560x1440 per eye) is what Pimax declared as the "target" resolution. Then possibly add to that extra SS to enhance the image. I too have been struggling to understand how the work load seems to have increased since I signed up for the 8K. But I think without SS it is still what I state above and in fact is what it always has been except for SS which I think is an option not a requirement. Some say that SS will be more than a nice-to-have and they are probably right. We'll have to see.
StreamVR says my system can handle (recommended SS) 5,079,888 pixels per eye which is about 1.4 x 3.7M so I'm hopeful I'll get a fair image. But in reality my favorite game is a monster FPS eater and I'll prob have to settle for less SS. Maybe Brain warp will come to my rescue!