I have an old 12 Core MAC PRO 5,1 running MAC OS 10.10 with a AMD RADEON HD 7950 3200 MB Vid card! Will the newer Dell Marketing USA LP Ultra Sharp 49" Screen Led-Lit Monitor Black (U4919DW) run with my MAC PRO?
HD 7950 only has a maximum 3840 x 2160 display through Mini Displayport. The U4919DW required Displayport 1.4 which allows 5120x1440 connection.
The most economic and compatible card with a 5k display are Polaris cards such as Radeon RX 480/570/580, but it required at least 10.12.6 OSX to support those graphics cards.
I bought a Dell 4k 32" monitor for my wife, I thought she needed to be able to run two HP notebooks using the one monitor, the Dell could do that. (She hardly has used that though ... )
It was a fair bit cheaper to buy two monitors to get the same screen space. If you want to save money, consider two lower resolution monitors. There often is a sweet price/performance spot for monitors, and the very wide ones are still well out of the sweet spot for value I think. But check if the HD 7950 will handle their resolutions.