No sluggishness in my retina imac. What it has done is ruined any chance of looking at a non retinal imac again. After using the 5k, the normal imac looks bloody awful. Just sayin...
I bought 2 refurb 5k base units. Upgraded both to 24GB of ram. I notice the same issues many have reported, in terms of mission control etc. It seems to me that there is a software issue there, and yosemite needs some graphics tweaks to optimize it. Hopefully those are coming.
What I will say is that Im pretty sensitive to performance issues. I work fast and I like/require a very smooth machine. The base 5k, is not smooth, and there a lot more "freezes" for performance related things, even with the extra ram. While I pissed that this machine feels slower than my previous core i7, There is no way I would go back to a non retina screen. Its just a zillion times better. The base unit is still faster on paper than my old i7.
I bought the base refurbs because they were 100 bucks more than a comparable i7 from last year, and Im glad I did. I could have spent another 800 odd dollars on the i7 with the bigger graphcis card, but I honestly dont think that will make the difference I would be looking for.
When the next 5k unit comes out, ill spring for the high end version of that assuming the graphics card is a monster. If not I may wait until that happens, but I cannot recommend the 5k enough.
If you do video for a living I think still worth it, because of the realestate and 4k options, but go for an ssd and max out the machine to minimize issues.
if you are on the fence about high end i7 or base 5k, go with base 5k. It might piss you off a bit here and there, but its such a next level experience to go to 5k youll be glad you did and the small issues wont bug you that much. Like I said though ill probably sell my retina in a few months and pick up the new one. resale on a retina will be higher I think than on the old display units.
980mx would be awesome