My first attempt at updating the display drivers for my iMac 5k 27" led to a Neon Plasma startup of a black screen with a blinking cursor.

Now, at the moment I am using the drivers that were auto-installed but only have a max resolution of 3840x2160. This of course is more than sufficient for my needs, BUT, the display is native at 5120‑by‑2880. So, I need that!

Is there a way to get the display to this native resolution. And if so, any advice as to the drivers I would need would be appreciated. I've done a fair bit of internet sleuthing but haven't really found a definite answer and would rather not go back to that terrible blinking cursor.

Again, thanks for the help.

Edit : Forgot to mention, the graphics card is AMD Radeon R9 M290X. Important bit.

There's a lot You could do, but first of all You should do this:

$ xrandr
Screen 0: minimum 8 x 8, current 1920 x 1200, maximum 8192 x 8192
LVDS-0 connected primary 1920x1200+0+0 (normal left inverted right x axis y axis) 262mm x 324mm
1920x1200 60.24*+

If You look, You can see: "262mm x 324mm"
That means: More high than wide.
This is obviously wrong.

Reason: Faulty firmware in Apple's builtin display.

A clear case of Apple cr@p.