4.0 is slow compared to the latest development builds and older builds like 3.5 and 3.0. If you upgraded (or downgraded) to 4.0, you're going to take a performance hit. If you're using an extremely old build of Dolphin and coming to 4.0, you're not going to get good performance because 4.0 is more demanding than previous versions before it. The latest development builds tend to be faster than 4.0, 3.5, and 3.0, so you would do yourself a great favor and use those: https://dolphin-emu.org/download
Dolphin has a dual-core option is that's what you're looking for. It is enabled by default. If you're talking about the OpenMP option, it should still be available in 4.0, but it's more placebo than anything except in a limited number of cases.
Dolphin has a dual-core option is that's what you're looking for. It is enabled by default. If you're talking about the OpenMP option, it should still be available in 4.0, but it's more placebo than anything except in a limited number of cases.