I recently upgraded my GPU to an Nvidia GTX660 (edit: was 640) to support 4k@60Hz, and it looks and feels absolutely amazing - but I'm taking a severe performance hit on text rendering, which is a problem when running Xcode full screen at 4k, which is what I do most of my day. My CPU is a Core i7-870 running at 2.93GHz, which although it's nearly 5 years old, is still a solid CPU as far as I understand it. I'm running off an SSD, I have maxed out the RAM with the fastest DIMMs that the system will support (1600MHz), but it's still not fast enough. So I'm looking at buying a new system, but on clock speed alone, the new iMac Core i5 with Retina display doesn't actually look that much faster than what I have (3.5GHz vs 2.93Ghz). Has anyone gone a similar route? I mean, 2010-era Mac upgrade to 2014 era with similar clock speed - do you really notice a performance boost, even if the clock speed of the CPUs stays roughly the same? Edit: Derp! I had the card in a PCIex4 slot. Put in a PCIex16 slot, everything is fine.