My employer took took a shipment of fifteen Dell computers a few months ago - with ATI Radeon HD 8570 graphics cards (3 years old, with DP 1.2 and 4k support so not obsolete by any means, and certified for Ubuntu 14.04 [1])
Then Ubuntu 16.04 comes out, and guess what? No fglrx driver support any more [2] and users report the open source drivers use about a core and a half worth of CPU, slowing down their entire machines. Apparently our only options are to buy new cards or stay on 14.04 indefinitely.
Meanwhile, I had an nVidia card and I was able to upgrade to 16.04 with no problems at all.
This week you might have resolved not to buy from nVidia - but in the same week I've resolved not to buy from ATI.
It's weird that you're seeing such high CPU usage with the open source drivers. AMD has been directly supporting them for a while now. For most applications radeonsi (the open source driver for GCN arhictecture cards) performs within spitting distance of the proprietary driver and for some the performance is better. I suppose it's possible they are more CPU intensive generally, but the kind of slowdown you're seeing seems pretty excessive. What applications are you seeing this problem with?
Ubuntu 16.04 does ship with a pretty old version of Mesa (full major version behind, about to be 2 major verions as Mesa 13 is in the RC stage) which probably isn't helping matters. Unfortunately, while there are some PPAs that make it fairly easy to install a bleeding edge build, there's not really a convenient way to install the latest stable release.
For some context, the reason fglrx/Catalyst has not been updated is due to an in progress driver transition for AMD cards on Linux. Generally speaking, Linux video drivers are split into a kernel part and a user space part. For quite some time, AMD has maintained two completely separate driver stacks on Linux. For the user space side, this didn't represent a huge amount of duplication of effort as most of the code is shared with the OpenGL portion of their Windows driver, but for the kernel side it was a bunch of wasted effort. A while back, they started on a new open source kernel driver, called amdgpu, that could provide the necessary facilities for both their open source and proprietary driver efforts. The new proprietary driver (AMDGPU-Pro) targets this kernel module. Unfortunately, amdgpu does not have production-ready support for GCN 1.0 GPUs like the 8570. This will get fixed eventually, but that doesn't really help you now.
I'll be buying AMD as well, the RX 400 series already piqued my interest but I can't justify buying another budget GPU from nVidia, even though the 1050 looks pretty attractive.
I wouldn't recommend that. AMD's software quality is horrible, and I'm saying that as an iMac user stuck with them on Windows. Whatever you think of nVidia, it's a breath of fresh air to see such polished auxiliary tools -- and yes, I think GeForce Experience is good... why? Living with AMD crap for years.
And if you think nVidia treats customers/users badly, just watch AMD's treatment of Apple hardware. They added artificial blocks preventing the "normal" driver from installing there (even though it is fully functional) and you have to use a special Bootcamp driver, which is incredibly outdated and buggy as hell in modern games. Their support is about as useful as you expect in a big corporation, and then some. It's so bad that enthusiasts are re-packaging AMD's drivers to have something: https://www.mxdriver.com
Not sure if this was rhetorical or not, but if it isn't, none of them. The 1070 and 1080 stand in a class of their own. AMD won't have a competitive card in these class until Q1 2017 which will be about the same time that the 1080ti drops.
I honestly don't care about this, these threads always attract those who value privacy above all else and believe that every should play on their terms. Most people do not care, and as an engineer I see extreme value in providing this data. This isn't to say that there aren't dark patterns being used here(the acceptance language is hidden in the EULA), but there is a simple work around...don't use GeForce Experience. Manually download the drivers from Nvida's website. In addition to there being a complete go around, I also use G-sync for my games which is superior technology to Freesync, so there is basically no chance that I'm leaving the Nvidia ecosystem unless they did something truly harmful to me.
Then Ubuntu 16.04 comes out, and guess what? No fglrx driver support any more [2] and users report the open source drivers use about a core and a half worth of CPU, slowing down their entire machines. Apparently our only options are to buy new cards or stay on 14.04 indefinitely.
Meanwhile, I had an nVidia card and I was able to upgrade to 16.04 with no problems at all.
This week you might have resolved not to buy from nVidia - but in the same week I've resolved not to buy from ATI.
[1] https://certification.ubuntu.com/hardware/201302-12679/ [2] http://www.omgubuntu.co.uk/2016/03/ubuntu-drops-amd-catalyst...