Illustrator CC is in Overprint mode super slow

I've been experiencing super slow performance in overprint preview mode for many years now, while using 4K screens. I noticed that it was much faster when I changed the resolution to 1080p, but the text became barely readable, so that wasn't a viable option. However, I recently discovered that when I resize the Illustrator main window to less than a quarter of the screen, the performance improves significantly. For instance, I can disable a separation and see the result immediately. But when I resize the window to anything larger than a quarter of the screen, the performance slows down again, taking about three seconds to see the result after disabling the same separation.

I work in a Prepress department and I just got a new 5K iMac. I have to verify colors in Overprint mode regularly, and now I have to keep switching between CPU and GPU modes in order to work.

I really don't think this is any kind of issue with what documents are open, because it still runs slow in overprint mode even with a blank document!

I'm not sure why the CPU can't handle overprint mode on my iMac. It has an Intel, 10 core i9, and I have a Windows PC at home with an 8 Core i9 with a 4K Ultrawide and the same documents run fine in overprint mode. In fact, there's little difference in performance between the two modes on the Windows machine. The only reason I could think of is if the new iMacs have an issue with proper cooling, which would slow down the CPU. I think the i9 is fast enough to smoothly move around a blank document, even on a 5k screen!

i have the same problem on iMac Pro (2017) 

3.2 GHz Intel Xeon W

32 GB 2666 MHz DDR4

Radeon Pro Vega 56 8 GB

I've found that little things may help with the performance of Illustrator in overprint preview, try the following:

1. Close your links palette (or activate a different tab within the same palette, hiding the links)

2. Close/deactivate navigator panel

3. Open Panel Options in the Layers palette and turn off all thumbnails

Those things I've found, especially with the Layers thumbnails and links palette, really help working in overprint preview better.

Another possibility is working off your own hard drive as opposed to files over a network (like some companies do).

Finally, if the problem still persists, it could be one or both of the following issues:

1. CPU is not up to snuff (underpowered), since all views except GPU Preview run off it

2. OS compatibility issue (some of my coworkers are experiencing annoying issues with Sierra but I'm doing ok with Yosemite so far...and it helps I'm the only one with a Mac Pro instead of an iMac)

Got the same problem here! I'm working on a brand new iMac ( iMac (Retina 5K, 27-inch, 2017) ) with Illustrator CC all up to date and every single time I put the overprint preview on, illustrator just get very slow.

What I don't understand, is that before in CS6, on my older iMac, I never have such thing to happen.

I asked Adobe to try to resolve my issue with a remote session, but after an 1hour with them playing on my computer the only thing they could come up with is that nothing can be done. They asked me to upvote your discussion so that some one eventually look deeper into this...

Did you try to deactivate the GPU performance?

That's from Preferences, then from your left choose performance, then uncheck GPU performance

Or click on rocket icon placed beside the menus, then uncheck GPU performance

Restart Illustrator!

i think you will going fine

Regards