The PDF rendering engine of Adobe is, since ever, one of the worst engines there is and I doubt this will ever change. I also got a fast PC with lots of RAM, but opening a computer mag with many graphics on the front can be so slow that you can see the single parts pop up. It doesn't seem to matter what graphics card you have installed.
"Is this something where the Adobe apps are not optimized for the 5K screen?" Of course not. Not yet. The new Mac is only out a few weeks and this has very low priority, I'd say.
No one else experiencing this? There is a long thread about illustrator with maybe one mention of indesign. I have had 3 iMac 5Ks (maxed out specs) now and all three suffered and were painful to use, running slower then a mid 2012 retina MacBook Pro. After 3 I started to rule out hardware and the iMac itself, everything else ran great except Indesign and Illustrator. Would be nice to hear something from Adobe on this. I am guessing they are not utilizing the ATI AMD gpu properly?
Hey, all of my Adobe products run in the range of extremely slow to unusable; InDesign is by far the worst. Like you, I run a decked out 5K iMac and Adobe CC 2014. Oddly most people have problems with Illustrator, however I find Illustrator to be usable, yet InDesign and Acrobat are nearly unusable. I would do anything to get rid of my iMac and get my much faster 3 year old iMac back.
Adobe has mentioned they are working on a fix for Illustrator however I have not seen any mention of InDesign. I suspect they will apply the same fix across the board if there is a software fix for this. Apple quadrupled the number of pixels on the iMac screen and that is a lot to ask of Adobe CC.
Also running an iMac with the GPU upgrade, and haven't noticed performance problems, yet! I'll test some of the issues mentioned here. My real problem is with the on-screen font rendering. At the 2560x1440 HiDPI, a page at 100% is just weak, like page printed without enough ink. Panning and zooming is a little laggy, too. At 2560x1440 (non HiDPI), everything is fantastic, although the rendering is a little rough (strangely not so on regular GPU on same machine). CS6 is perfect in every way! Oops, I guess unrelated, but I wanted to see what others are experiencing.