Driver-based downsampling (VSR) is still not available for most AMD GPUs (your R9 280 is one of those [still unsupported] cards).
You'll have to wait for the next version of the "Omega" drivers to get that feature.
But 6xIR in Dolphin works well and it's faster and more stable than any kind of driver-based downsampling.
If you don't like editing .ini files and want that feature integrated into the UI, you can use this custom build of Dolphin:
https://forums.dolphin-emu.org/Thread-unofficial-ishiiruka-dolphin-custom-version
It goes up to 8xIR (that's 5K res.).
P.S.
Performance Guide updated to v0.985:
https://forums.dolphin-emu.org/Thread-unofficial-amd-ati-gpu-performance-guide-feat-dolphin
You'll have to wait for the next version of the "Omega" drivers to get that feature.
But 6xIR in Dolphin works well and it's faster and more stable than any kind of driver-based downsampling.
If you don't like editing .ini files and want that feature integrated into the UI, you can use this custom build of Dolphin:
https://forums.dolphin-emu.org/Thread-unofficial-ishiiruka-dolphin-custom-version
It goes up to 8xIR (that's 5K res.).
P.S.
Performance Guide updated to v0.985:
https://forums.dolphin-emu.org/Thread-unofficial-amd-ati-gpu-performance-guide-feat-dolphin