GI Cache quality is probably not helping you much here, and likely adding render time. If you are not already using Defer Atmo, enable it. With 32 atmo samples if the noise is coming from the atmosphere it should resolve that at AA4 (again, with Defer Atmo enabled). If the noise is from clouds and you are using V3 clouds (any of the Easy Clouds or Generic cloud presets), try increasing the Voxel Scattering Quality in the GI settings of the Render node, GI in Clouds tab. Test a value of 200.
- Oshyan