Edit: The new Bootcamp drivers set includes the Radeon drivers, and every other drivers seem to work fine so far. You need to get them using the Bootcamp Assistant. I did a lot of trial and error. I reinstalled 8.1 fresh because my preivous install didn't want to upgrade, then updated to 10 on that fresh install. Once I had done that, I tried to reinstall 10 clean from my USB stick made with the Microsoft tool but it didnt want to activate. Thats strange because when you upgrade Microsoft is supposed to store the computer's generated hash code to activate whenever you reinstall Win10 on that computer.
I ended up reinstalling Win8.1, and reupgrading to 10. I'm not touching that thing anymore! So I wanted to try this solution but then something interesting happened to me. I dunno how this happened but I reinstalled Windows 10 from the ISO on Microsoft's website and the graphics drivers seems to have updated itself.
Radeon 6570 Driver Download
By that I mean no installing of special drivers or screwing around with driver packages. After initially corrupting my OSX system folder while trying to reinstall Windows 10 (had the prohibitive symbol show up) and recovering my OSX partition, I ran Boot Camp Assistant again and re-downloaded the Boot Camp Support software to my bootable USB along with the Windows 10 ISO. After rebooting and skipping the part where it asks for my Windows 10 key (my Win 8 key didn't work so I just skipped it) I formatted the BOOTCAMP partition as usual and installed Windows. After going through the initial setup I logged in to the desktop and completed the Boot Camp Support Software install. Lo and behold, my AMD graphics drivers were already installed and when checking Catalyst Control Centre (no errors btw) it says my Driver Packaging Version is -150715a-186304C and my Catalyst Control Center version is 2015.0715.2138.37093.
Radeon 6570 Review
What is latest driver for AMD Radeon HD 6570? This is how you select the correct driver for your desktop computer Download Drivers. AMD Radeon HD 6570 video card drivers. Install drivers automatically. DriverPack software is absolutely free of charge. Available drivers (3) all systems. Windows 10 x64. Windows 10 x86. Windows 8.1 x64. Windows 8.1 x86. Windows 8 x64. Windows 8 x86. Windows 7 x64. Windows 7 x86.
Even stranger is the fact that my Windows 10 was already activated and didn't require a key. I assume this is because when I initially upgraded my Windows 8.1 Boot Camp install it tied my original Win 8 key (which I have a disc for) to my machine, thereby allowing it to get the Win 10 upgrade for free. Unfortunately, no native 5K resolution yet as far as I can see. My suggestion for a potential fix would be to try and reinstall Windows 10 completely and actually download the very latest Boot Camp Support Software to your bootable USB via the Boot Camp Assistant application. Obviously OP's solution is still valid as this will work perfectly if you have already installed heaps of software and don't want to reformat/reinstall Win 10.
I haven't tested any games yet and haven't checked out the support software install folders, I will update this post with my findings in the week when I have a day off work and perhaps upload some screenshots. Tl;dr I got my AMD Drivers to work by simply reinstalling Windows 10 from scratch with an ISO downloaded off the MS website converted to a bootable USB (with Boot Camp Assistant), and also ensured my Boot Camp Support Software was downloaded to the USB.
. Processor for ultrathin notebooks' defined as 15W typical TDP. 'Class' for 'best-in-class' defined as an ultrathin notebook.