So the op isn't getting it done

[DavidEccleston]

Lightroom, and I would assume Photoshop, can get a decent speed boost from fairly low-end graphics cards with only a few processing cores, so I wouldn't worry too much about that specs when deciding card to get. You don't need an nVidia GTX 980, or GTX Titan or anything like that. You can get away with the lower-end cards. What you *do* need to check is that the card can support your 4K display, both in resolution, and in connector type. Typically you'll find your perfect monitor first, then choose a suitable graphics card to match it. As you'll see below, an nVidia GT 720 ($50) could be all the GPU you need.

Assuming you go with an nVidia card, you can check the specs on each card on their site, right here. Choosing a modern (700 series), low end (ie: lower numbered) card at random, I pick the GT 720, then specifications. I see 192 CUDA cores (graphics cores that Lightroom can make use of... 192 is plenty), 3840x2160 (4K), but only 30Hz with dual-link DVI, and 60Hz if you can find a display-port version. (this is in the fine print at the bottom). nVidia makes the graphics chip, but other vendors make the actual cards. XFX, EVGA, ASUS, etc. A quick search on Amazon, and I can't find anybody offering this card with a displayport variant. So if your monitor of choice needs displayport, you're out of luck on the cheapest card.

Next, I select the GT 730, select specifications. I see there are 3 versions. One supports 2560x1600 (not 4K), while the remaining two support 3840x2160 (4K), and each have the same caveat about 30Hz on dual-link, vs. 60Hz on Display port. You can also see the 2560x1600 version only has 96 CUDA cores, while the other two versions have 384. I would bet that the worse version is actually a re-branded 600 series chip, and doesn't meet your 4K needs, while the other two should be fine, if we can find the right connector... which I can't if you need display port.

Moving up to the GTX 750, I can finally find cards offering display port, though they're now in the $130-$150 range. The card should easily handle anything you throw at it, unless you're doing serious gaming (no cards, even the $1000 GTX Titan cards are very good at 4K gaming).

[Busted Knuckles]

David, thanks for the research - GTX 750 or better and the box is checked.

The point on the 4k monitor is the first thing to choose as it is the key "human interface" element .

Again, thanks for the research and thoughtful advice.

I get lost in the bits and bytes just a bit sooner (or would that be a byte) than JRW.

Mike

[Busted Knuckles]

I picked up a Dell laptop w/ a 4k screen and the ability to push 4k out the HDMI port. Not quite the monster desk unit, but at this point is the shared laptop w/ my wife (pay bills on, general surfing etc). Will see if is enough.