I also have performance issues since the upgrade to F42. Can you elaborate yours a little more?
In my case, applications/processes freeze for several seconds, but always in an isolated manner (so everythin else keeps working responsive). So far I had freezes of around 10 seconds of kate when I clicked in the text window to write something, Firefox when opening new tabs, the WiFi itself (I presume that was wpa_supplicant), and the sleep mode (when initiating sleep, the screen goes locked and freezes around 10 seconds before finally going sleep). Also, the desktop/KDE itself can freeze, and at a boot, I had the same issue with cryptsetup that did not respond some time until my encrypted disks had been decrypted and subsequently mounted (I already feared the system no longer boots 
). But in all cases in which I could test it (firefox, desktop/KDE, kate), everything else worked fine and I could still do other things while they had been frozen.
My logs only indicate that processes sometimes don’t respond for some time, but at first glance not much more. However, I have not yet done a sophisticated check of what is going on, and did not yet review logs in detail. But when I saw your topic, I wanted to roughly summarize my case and see if that is about what you experience?
I have no taints in the kernel (taint = 0) and no nvidia, only default Fedora repos plus the mesa drivers from rpmfusion (I limited rpmfusion to these drivers’ packages). AMD Ryzen 7 PRO 6850U with Radeon Graphics. 6.14.2-300.fc42.x86_64. I have no swap but 32 GB RAM, which definitely is more than a normal Fedora installation needs. F42 KDE, originally installed at the time of F37. I hope I can spare some time in the next days to check this out more detailed, but my time is slightly limited these days
Anyway, would be good to check out if we experience the same thing, and see if we can identify (maybe also with others) what those who experience this issue have in common.
Supplement: I added kernel and KDE for now, the first as this could be linked to a kernel issue (including your elaboration as far as known), and as long as we cannot link it to something that explicitly is related to only Workstation, performance issues like ours are likely to be not linked to the DE, so it might be useful to also lead KDE people with performance issues here so that they can compare. I can split the topics later if we find out that its different. I hope that is in your interest too, otherwise I can remove it again - its your topic
If we find out that your issue is the same as mine, I suggest we remove nvidia (which I do not yet do to keep focused on your case), as it then is likely to be not related and only distracts in such a case.