I am not sure where to post this, I've been looking for a solution since 2 weeks and nothing, none, nada, null, zero.... I came from late 2009 ( core i5 / 8GB RAM / 4850HD ) running 10.8.5 and paid $4000 for an i7-4771 / 32 GB RAM / GTX 780M / PCIe SSD. Eagerly unboxing the iMac, I power it on, Mavericks 10.9 preinstalled. Cool... Software updates ( 3GB including 10.9.1 and some apps ). So far so good. Spent couple of minutes working on it and I was like.. WTF is this thing ? Applications open instantaneously, everything is very quick. 750MB/720MB read write speed ...................................................................... BUT The UI is freaking slow !! it's not that I get any beachball whatsoever but it's nothing close to fluid I am always under the impression that the video card is having hard time or CPU load is 100% but I have 28 GB free ram, CPU idle 98%, no apps installed ... just nothing. Hardware test reported NO ISSUE. I can't believe that my late 2009 felt more responsive when doing barely nothing. So I installed Windows 8.1 via BCA and TADA! Everything is just perfect. I did a clean boot and no help. What's the deal ? Also HD recovery is very sluggish and tearing is unbearable. With 10.8.5 I had no issue Here's a video : http://www.youtube.com/watch?v=lJO4wnRMCYg I run Unigine Heaven Benchmark and I noticed that the Max FPS is 60 whereas windows get over 200FPS. Has Apple capped the FPS with the new OS ? Too much heartache when you throw that amount of money on such a disappointing experience.