If your budget will cover it, you'd do much better with an i5 3570K/2500K and a z77/z67 motherboard. AMD CPUs have much lower single threaded IPC than Intel equivalents, and single threaded IPC is what Dolphin wants.
RAM wise, if it's cheaper, you may as well get something clocked at 1600 MHz, as you'll see approx 0% performance increase by raising memory clocks above this, both in Dolphin, and many other applications. Also, for Dolphin 4GB is more than enough, but you may want/need 8GB for other things. I'd only reduce to 4GB if you were desperate to save some more money.
GPU wise, I'd say an HD 7870 is definitely enough for 1080p. However, some users have reported unexpectedly low performance when using HD7xxx series (and occasionally GTX6xx series) graphics cards with the D3D11 backend. This houldn't cripple your rig, but if there was a similar performance HD6xxx series card at a similar price, I'd go for that instead.
RAM wise, if it's cheaper, you may as well get something clocked at 1600 MHz, as you'll see approx 0% performance increase by raising memory clocks above this, both in Dolphin, and many other applications. Also, for Dolphin 4GB is more than enough, but you may want/need 8GB for other things. I'd only reduce to 4GB if you were desperate to save some more money.
GPU wise, I'd say an HD 7870 is definitely enough for 1080p. However, some users have reported unexpectedly low performance when using HD7xxx series (and occasionally GTX6xx series) graphics cards with the D3D11 backend. This houldn't cripple your rig, but if there was a similar performance HD6xxx series card at a similar price, I'd go for that instead.
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