I have an HP Z800 with two Westmere EP based X5670 CPUs (basically gen 1 iX series) and an HD7950. I don't know when exactly this started, I've been switching between various distros probably a bit too much. I'm currently on Antergos with the base install option because it's easy to nuke and reinstall quickly to remove variables (though I keep track of exactly what it installs), but this also happens on vanilla Arch and this issue has also seemingly started to show up in Ubuntu as of late. I haven't yet tried Fedora, but I suspect it is similar.
Basically, the system keeps stuttering and hanging. It generally seems to line up with each second, but can be somewhat inconsistent depending on tasks I'm engaging in. It shows up a ton when I have updates running and try to scroll in a browser or move windows around. When I attempted to use DDE the system became practically unusable for anything, but it occurs on Gnome on Xorg, KDE, and Gnome on Wayland as well. I've tried both the amdgpu and the radeon driver, doesn't seem to make a difference.
Is there any chance this could be related to Meltdown/Spectre patches with regard to context switching? If so, is there any way I can combat this, even at the expense of some theoretical performance?