In searching for an answer, I found this article on PCI bandwidth utilization
. It seems to suggest that a video card that normally requires 16x will scale down to the number of lanes actually available. If I am understanding this correctly, this should mean that I can use a 16x card in a 4x slot but with less performance. I'm not really concerned about speed in this case since this display will not be used for gaming.
I guess the only other thing to determine is whether a 16x 2.0 card will work in the 4x slots of these particular boards. The manual doesn't indicate whether the 4x slot is 2.0 or 1.0. Or does that not matter?