Very interesting, thanks for the info. But that would mean I'd need a computer with Skylake right? Would it work on Haswell with TB 2?
From your original post I'm not sure if you're talking about an iMac with additional external monitor, or a MacPro, but either way YES, in a normal straightforward set-up, to display 5k you need TB3 (which has now switched to the new USB-C connector btw), which will show up on Skylake.
But if you must, 5k can however be accomplished with Haswell if you have at least two TB2 ports (which incorporate MiniDisplayPort 1.2), using a
dual-cable DisplayPort setup.
Personally I'm very excited by the new USB-C standard which is supported by over 700 companies, and these
reversible little ports are going to show up on just about anything from desktops and laptops to peripherals and cellphones. Now that the latest ThunderBolt iteration has switched to the USB-C connector, the debate over TB vs USB can finally be over, and everyone can enjoy their preferred interface, whether that's USB3.1 or ThunderBolt 3, the USB-C connector does it all, DisplayPort, HDMI, 100 Watts of power, USB, and VGA or Ethernet.
USB-C is all set to become the premier connector for the foreseeable future. TB3 over USB-C is still at the top of the heap as far as speed and bandwidth are concerned but with expected licensing fees and the price of the chips to still be pricey, it will probably remain more of a professional solution, with many people instead opting for the cheaper USB3.1 interface. Exciting times.....