MacOS – How to get full resolution out of different generations of cinema displays

After more playing around, I now have a workaround whereby using a Mini DisplayPort to VGA adapter instead of one of the Mini DisplayPort to DVI adapters, i.e. an analogue connection to one of the displays instead of digital, seems to work and allows me to have 3 active displays configured like so:

Display 1 connected via HDMI to DVI adapter (into HDMI port)

Display 2 connected via (passive) Mini DisplayPort to DVI adapter into Thunderbolt port 5 (as in the diagram in the above article)

Display 3 connected via Mini DisplayPort to VGA adapter into Thunderbolt port 2.

However, I was hoping to have an all-digital solution as the above Apple article suggests I can, so I'm still hoping someone will come up with a better idea!

UPDATE: This appears to be an issue introduced with OS X 10.9.3. Tried an identical machine running 10.9.2 and the second configuration I tried in the original question worked just fine. Hopefully it'll be fixed in 10.9.4, until then the workaround above is still valid.

I am not sure about the GT120. However, per this post, yes can get full 4K resolution (3840x2160) @ 30Hz with the Radeon 5770 and an ACTIVE Mini DisplayPort to HDMI connector that supports 1.1 and not just 1.2. However, this will get you the full resolution, and not the 300dpi screen doubled "Retina" (aka HiDPI mode) experience. If you download SwitchResX it will list possible options for you.

I can confirm this worked perfectly to get both 3840x2160 and 1920x1080 HiDPI (Retina) with a Mac Pro, Radeon 5770, an Acer B286HK, and a regular mini-DisplayPort to DisplayPort cable.