I'm not using Vulkan / Metal at all -- It's Mac, running XP11 in Open GL mode. GPU is Sapphire 580 Pulse/Nitro, 8GB VRAM, CPU is 3.46ghz 6-core, with XP on an internal SSD. Usual fps is 40-50.
I am only getting SMP clouds when the Visual Effects setting in XP11 prefs is set to "High" or "Max" (HDR on) --which causes a massive FPS drop from about 35-40 to 18-20.
Please advise.