Late 2013 Mac Pro with Dell U4919DW 49 inch UltraWide screen?

MacBook Pro users are still fiddling with this display trying to get it to straighten up:

Dell U4919DW / MacBook pro 5k issue - Apple Community

Many Users on that discussion are stuck because it does not appear to be properly supported by Intel Integrated graphics, but others have not been able to see success without some of:

• using additional software

• Using Picture-by-Picture and TWO interfaces, each of which draws half the screen

• Using advanced versions of Apple beta software

HDMI is a "legacy" interface designed for HD TV 1920 by 1080p at best. It has seen a number of attempts to extend it, but it is a real balancing act getting all the right parts to work together.

The output of the Mac Pro 2013 HDMI port is not suitable for extra-large sizes like what you are attempting. I recommend you use a ThunderBolt/Mini-DisplayPort to Dsiplayport input:

Input Connectors

2 x HDMI 2.0 (HDCP 2.2) (10-bit color @ 60Hz)

1 x DP 1.4 (HDCP 2.2) (10-bit color @ 60Hz)

5 x USB 3.0 Downstream port

2 x USB 3.0 Upstream port

1 x USB Type-C (Alternate mode with DP1.4, Power Delivery, and USB2.0) (8-bit color @ 60Hz)

The state-of-the-art interface is DisplayPort (family). It drops the HUGE amount of 'heartbeat' refresh data required by CRT displays and simply sends the changes. That alone helps it to run faster and your computer to run cooler. Screen refresh comes from the screen's own internal buffer, and can be above threshold of perception for flickering..

Once you get on a DisplayPort interface, there may be a bit of software fiddling you still need to do to get 5K on that particular display. It appears the screen descriptor technology has 'run out of gas' and Apple seems to be working (at what seems to Users like slow motion) to come up with permanent fix.

The built-in HDMI port on the Mac Pro 2013 does not even 'properly' support 4K in that it is limited to just 30fps. It is possible to do 4K at 60fps on HDMI by getting a Thunderbolt i.e. Mini Displayport to HDMI 2.0 adapter like this one. See - https://www.club-3d.com/en/detail/2339/mini_displayport_1.2_to_hdmi_2.0_active_adapter/

It has been possible to connect the Dell UP2715K to the Mac Pro 2013 and run it in full 5K resolution. This required using two Mini Displayport connections with half the screen being driven by each connection. In theory it might be possible to do the same with with an ultra widescreen 5K display but I don't think it will be possible with the U4919DW since it only has a single Displayport connection.

Therefore on the Mac Pro 2013 the best you will get will be 4K resolution as you have found. I would expect the Mac Pro 2019 will have no problems at all.

Note: Officially Apple only support eGPU if you have a Mac with Thunderbolt3 however some people have managed to trick this in to working on the Mac Pro 2013. See - https://www.macworld.co.uk/how-to/mac/egpu-mac-3690094/

It's not going to work over HDMI. On the 2013 Mac Pro, you'll only get 3840x2160 or 4096x2160 at 30Hz which is unacceptably slow. The Mac Pro will support 3840x2160 at 60Hz over DisplayPort. Your 49" monitor is 5120x1440 which is fewer pixels than 3840x2160 so the Mac Pro definitely has enough bandwidth over DP to work...although you might need to use an app like SwitchResX to set a custom resolution. Dell's website says that DP 1.2 is sufficient to drive the 49" monitor at full resolution and that's what the Mac Pro supports via the TB2 ports.

Have you tried a miniDP to DP adapter? You'd connect the mDP side of the cable to your Mac Pro and the larger DP side to the monitor.

I'm running a 38" Dell monitor at 3840x1600 at 60Hz over DP from my 2013 Mac Pro and it works great. I'd be really interested to hear whether DP works on the 49" monitor.

Readers -- keep in mind:

When you specify SCALED resolutions, you can no longer read the actual physical resolution from the Displays control panel. Instead, to see the actual physical resolution, you must use other means -- such as "About this Mac".

When you specify SCALED. Apple sets the screen resolution to maximum. Graphics are shown at full resolution. But to keep text from being too small to read, it scales all text so that it "looks like" the numbers stated under "Scaled".

So "SCALED" 3480 by 1600 MAY be working correctly on a 5120 display. You would need to verify actual screen resolution by other means.

What cables and adapters are you using for what interface(s)?

External graphics requires ThunderBolt-3, and no adapters will get you true ThunderBolt-3 on your Mac Pro.