I have an early 2013 Retina MBP (16GB ram, 2.7GHZ, SSD) running Yosemite, and use parallels for software development on windows (win8 & 10). Performance doesn't feel great anymore, and the 2013 doesn't officially support 4K so i sometimes get a blank screen momentarily when using my external 4K monitor. I am considering upgrading to a 2015 Retina MBP that has the improved Graphics and CPU. I am interested to hear from anyone who has taken the plunge and gone for the 2015 model and is using it for heavy work (dev/ graphics / VMs etc.)... Is there a noticable improvement in performance in comparison to the older MBP models? if you use a windows VM, does it perform better?