What's the cheapest video card (used/new) for 4K?

[vcuares]

I have 3,1 2008 Mac Pro. I recently bought a $250 LG 24" 4k and it is awesome and "retina" like. I bought it mainly for the PS4 pro. I am also using my 2012 macbook air to drive it at 30hz 1080p HiDpi and I love how it is so crisp. I can switch native 4k on the MBA for situations I want more window space no problem. I mainly do lightroom and I have 8 active drives to get my files from.

I have 20" x 30" x 20" PLP it was the rage before, but now I'm moving on and going minimal. My new 24" is so thin and light compared to my old 20" which is almost 3 or 4 times the weight.

I have broken xfx 6870 that I can get an RMA for lifetime warranty, but I don't think this will work.

My questions would be.
1) will it drive it 60hz or 30hz? I'm ok either way, I just want to gauge price difference.
2) will Lightroom use it for HW acceleration?
3) Used or new is fine.
4) is it plug and play for El Capitan? (max OS version for 3,1) (i'm willing to flash)
5) should I just buy macbook retina that can drive 4k 60hz for $500-$600 used? and sell my mac pro?

 

[the_zee]

In my opinion optimal card would be flashed GTX 680 2GB. They are readily available from a number of sellers on eBay and fairly inexpensive.

answering your questions:
1. Yes, the card will drive 4K @60Hz via DispalyPort
2. Yes, some level of HW acceleration will be provided, with proper drivers installed.
3. Used and flashed from eBay runs just fine.
4. Yes, the OS provides basic drivers support for this card, but for optimal performance latest Nvidia web driver is recommended.
5. very hard to answer, everything is very individual and the matter of personal preferences. But from my experience, Lightroom even on a early 2015 13" MBPr with Core i7 and 16GB RAM sometimes painfully slow.