My boys are both around 6 feet but I am small (5'2") - a king size bed suits us just fine (although we can deal with a queen or even a double if needed). But I think the cuddle-ness factor plays a large role. MrS doesn't like to be crowded when he sleeps while Dude likes to sleep all intertwined. I prefer touching but not all tangled. So it usually ends up that I have my legs intertwined with Dude's but the top half free with a hand or foot just leaning up against MrS.
Another important factor is bedding - MrS and I learned years ago that we each need our own sets (since I am a notorious blanket and pillow hog) - so we generally have 8-9 pillows available and 4-5 different covers of various warmness/weight. So if someone wakes up and is too hot/cold they can fish around for whatever suits (or more pillows or whatever).
I find it interesting that, although I love my middle cuddle position, I am perfectly capable, apparently, of taking up an entire king-size bed BY MYSELF. (The boys also claim that my density increases exponentially in these circumstances...
Now FOUR in the kingsize bed does present difficulties...under these circumstances MrS insists on an "end" position and that the person next to him is ME (since I have learned over the last 20 years to sleep stretched up against him without either shoving him out of bed or tying us in knots...I'm his barrier against others).
(Dude is the most likely, however, to abandon the bed for the couch...MrS snores and, on occasion, he and I will have a competition as to who can outsnore the other...