Dell XPS 8700 and AMD FirePro W4100 Upgrade

I have a Dell XPS 8700 system that I need to upgrade the video to drive two 4K Dell monitors.  This is not a gaming system so I would like to keep the cost and power consumption down.  In addition, the ability to drive a third 4K monitor may become important in the future.

The cheapest solution to my problem seems to be the AMD FirePro W4100 2Gb Cards. Unfortunately, these cards are not specifically listed as compatible with the XPS 8700.

Questions:
1. Is there any reason why these cards would not work in an XPS 8700?

2. There seems to be multiple versions of the same card being sold by Dell.  In some cases the difference seems to be the bracket height, but otherwise there seems to be no explanation for the price difference.

Any clue why these parts have such different prices, and why the kit versions are cheaper?  Which one would be best for me?

http://www.dell.com/en-us/shop/accessories/apd/490-bcvj  (FH brkt $149)

http://www.dell.com/en-us/shop/accessories/apd/490-bcho   (FH brkt kit $119)

http://www.dell.com/en-us/shop/accessories/apd/490-bcvw   (LP brkt $189)

http://www.dell.com/en-us/shop/accessories/apd/490-bciy    (LP brkt kit $139)

Thanks in advance for the help