Hi all, Just wanted to share my experience with upgrading the CPU on the newest iMac 5K. I also upgraded the "Fusion Drive" to a standard 256GB SSD. I unfused it and I left the 128GB Fusion Drive SSD on the board. Stock CPU: i5-4690 Upgraded CPU: i7-4790K Stock HD: 1TB Seagate + 128GB PCI-E SSD Upgraded: 256GB Samsung EVO Pro + Stock 128 GB PCI-E SSD RAM: 8GB Stock Upgraded: 8GB Stock + 16GB Crucial RAM = 24GB Total. I've also attached the performance figures using GeekBench. If you're up for a challenge and not afraid of damaging your iMac, go for the upgrade. It is surprisingly easy once you know how to take the LCD off of the main frame. That is a pain because Apple uses adhesive strips. More details on the iFixit guide which is what I used to upgrade. Overall, it is not too difficult. Be careful and don't bend the LGA1150 socket pins but even that could be fixed (with a lot of pain). Cheers lads and happy holidays!