Bear in mind that if you render an IR above your monitor's native resolution, Dolphin applies a pretty poor scaling filter to make it the right size to display. I'm pretty sure the one we use for SSAA is better, though. That should mean that you end up with better image quality with an IR that matches you monitor and Dolphin's SSAA turned up high.
Also, I don't think any games Dolphin emulates have detailed enough textures for SSAA to be needed at high IRs, so you can probably get away with MSAA in compatible games. MSAA is like SSAA in that it renders at a higher resolution when considering which triangles occupy which pixels, but it only colours things in at the output resolution (it generates one colour per pixel per triangle, but considers the colours of multiple triangles in pixels with multiple triangles). The result is that pixels with edges get anti-aliased, but those that don't have edges don't get anti-aliased. Those pixels shouldn't have aliasing anyway under most situations.
Also, I don't think any games Dolphin emulates have detailed enough textures for SSAA to be needed at high IRs, so you can probably get away with MSAA in compatible games. MSAA is like SSAA in that it renders at a higher resolution when considering which triangles occupy which pixels, but it only colours things in at the output resolution (it generates one colour per pixel per triangle, but considers the colours of multiple triangles in pixels with multiple triangles). The result is that pixels with edges get anti-aliased, but those that don't have edges don't get anti-aliased. Those pixels shouldn't have aliasing anyway under most situations.
OS: Windows 10 64 bit Professional
CPU: AMD Ryzen 5900X
RAM: 16GB
GPU: Radeon Vega 56
CPU: AMD Ryzen 5900X
RAM: 16GB
GPU: Radeon Vega 56