I picked up a FirePro W4100 with 4 ports on eBay for around $50 before I saw your post. It's an official Dell supported card for the 5810. I read there may be a slight chance of system stability issue if you run 2 cards when you can go with just 1 for not a whole lot more. Let's see how that works out. Thanks.
The advantage to running a quad port card is that all of the VRAM is available for the display. When you run 2x dual cards, the memory usage is unequally configured between the cards and restricts part of the VRAM's allocation. That may or may not have an operational impact.
)... I upgraded my video cards because the VRAM in the 295 is only 256MB. UHD monitors require more. The NVS 310 is available in 512MB and 1GB. The P620, a quad, has 2GB... which is probably the minimum amount of VRAM anyone running 4 hi res monitors should consider.