Adding a 4K 2nd screen to a 5K iMac

[Sakurambo-kun]

I've just got a shiny new 5K Skylake iMac and I'm using my old 27" 1440p Dell screen as a second display. It's fine for what it is, but I'm wondering if I should upgrade it to a 4K display. (I'm assuming there's no way to add a 5K display)

My questions are - what will happen to the scaling on the 4K screen? Will everything just get bigger as it slides from my primary monitor to the 2nd screen? Or will it be scaled somehow to retain consistency? The nice thing with my old 1440p display is that the physical size of things is the same on both screens.

And from a purely aesthetic standpoint, can anyone recommend a 4K display which sits nicely with a 27" iMac?

Thanks all.

 

[gymrat2k]

The item that is moved will stay at the same relative size. If it is 1920x1080 "effective" pixels on the external screen, it will be that on the iMac screen also: http://imgur.com/a/PKjKe

iMac 27": 2560x1440 pixels (109 PPI)
iMac 5K 27": 5120x2880 pixels (218 PPI)
External 40": 3840x2160 pixels (110 PPI)

When measured with a ruler laid on the screen, the length and height of the images below are almost identical.

"As with all other Apple products with Retina-class displays, the iMac display is used in HiDPI mode, where the native horizontal and vertical resolutions are exactly halved as far as the user is concerned. So here the 5120 x 2880 pixel counts are rendered on-screen like a 2560 x 1440-pixel display.

That 2560 x 1440 resolution is the same size as the previous 27-inch iMac models, and so the true 218 ppi pixel density appears to the user like the 109 ppi desktop of the non-Retina iMac – but with all screen fonts and graphics effectively rendered much sharper."