Normally, on setups like that, a not all of the video cards run at x16 mode. Some will run x8 or x4.
Thanks for the responses bert and blaznazn. My first thought was when seeing 3-6 card setups was, those motherboards must cost a small fortune to have that many x16 slots. I looked into it, and it seems several individuals claim that for this, x1 vs x16 makes no difference. The reasoning I can see this as a reasonable assumption/statement is that many also seem to 'know' that the ram on a video card is not important, it doesn't seem to matter how fast the ram is either as -everyone- underclocks- the ram, in many circumstances, they do so to radically low levels to generate less heat. How I understand it, the number after the x in the x1 or x16 or whatever is a reference to the data transfer rate. Bitmining doesn't load massive amounts of data, it requires massive amounts of calculations, I could be wrong, but that is what I've come to understand.
It sounds like it is being suggested that if you have enough power (easy to do) and are capable of keeping all of the cards cool enough, then all 4 cards should be running at their maximum. But these circumstances are seemingly never met?