PCSX2 settings for smooth performance on a mid-range PC?

Leave most things on default, the current builds are well tuned. The ones that matter: renderer on Vulkan or Direct3D 11/12 (try both, one is usually smoother on your card), internal resolution at 2x or 3x rather than 4x+, and keep speedhacks at their defaults. If a specific game stutters it's usually that game, not your settings, so check its compatibility notes before changing everything.