7490 Dual Monitor Set up issues

@Jxhenderson  Ok, quite a bit to unpack here.

First, the display model absolutely can make a difference.  Next time it might be worth mentioning that before the very last sentence of the post.  If your results had only been experienced when using a WD19 and a WD15, then I would have said that the likely issue was that even if you are selecting 1920x1200 resolution, Windows may only be changing the render resolution, but not the active signal resolution, i.e. the system would still be sending a 2560x1600 signal on the wire, in which case you wouldn't be freeing up any actual bandwidth by using a lower resolution, and that might then be why you can't achieve 1920x1200 on both displays.  The way that could potentially be fixed would be to set the resolution using Intel HD Graphics Control Panel / Command Center rather than Windows Display Settings.  But you also mentioned using the TB16 and the D6000.  They both operate in completely different ways from the WD19/WD15 and even from each other.  The TB16 should allow dual 4K 60 Hz or even triple QHD from your system if it has Thunderbolt, and the D6000 should allow dual 4K 60 Hz + 4K 30 Hz all through the dock even from a non-Thunderbolt system thanks to its use of "indirect display" technology called DisplayLink -- not to be confused with DisplayPort.  I'm also not sure what you mean that using the built-in HDMI output caused the display to "not appear to be anywhere close to the resolution of the DisplayPort display".  The HDMI output on the 7490 and the HDMI input of the UP3017 both support HDMI 1.4, which is enough for 2560x1440, but I'm not actually sure about your display's native setup of 2560x1600.  Not all displays support their native resolution and refresh rate on all of their inputs, and typically it's HDMI that can lag behind simply because historically, HDMI has lagged behind DisplayPort in terms of capabilities.  But just to be sure, did you actually check Windows Display Settings to verify that the display connected that way was in fact running in that mode when you had it connected via the system's HDMI output?  And also make sure it was set to the same scaling setting as the DisplayPort display?  If all of that looks good, then I'm not sure exactly what you mean by your description.  Maybe posting a photo of the differences you're seeing would be useful.

But if you want to get both displays running through a dock for convenience, first of all I really wouldn't recommend running 2560x1600 display at 1920x1200.  A 30" display using only 1920x1200 resolution results in only 75 pixels per inch.  The Windows reference standard is 96 ppi, just for context.  So that alone is going to result in fairly grainy looking text, and on top of that, you'll have the additional scaling issues caused by the fact that you're mapping a 1920x1200 signal onto a 2560x1600 physical pixel grid, and the former does not map cleanly onto the latter.

So I would focus on getting a setup that allow you to run both displays at their native resolution.  You'll get a much sharper image and much more workspace.  For that, the TB16 would be the ideal choice, with the D6000 being the fallback if the potential drawbacks of DisplayLink technology are acceptable to you (which I wrote about in the post marked as the answer in this thread.)  But I would suggest that you focus on one of these dock choices rather than trying to troubleshoot four very different dock models.  With the TB16, I would suggest using the DisplayPort and Mini-DisplayPort outputs, and with the D6000 I'd suggest using the DisplayPort outputs and also making sure you have the latest DisplayLink software direct from DisplayLink.com.