This is not what you want to hear, but alas no. I still get spikes, but I no longer notice them and games don't studder on me. Let me see if I can find the thread(s) that I used to get here. I also noticed that being on the 6.9 betas made it better, but if you read the second thread you will see that unRaid is not 100% leaving the isolated cores alone, even when the VM is powered down. I'm on the VM right now and in task manager it says that my CPU usage is around 10%, but unRaid is showing all of the VMs used cores around 20 to 25% usage. The 3900x has enough power with some of the fixes in the below threads to "power" through the extra load, but older CPUs might not be able to. It's also worse on Ryzen 2 CPUs at the moment due to a bug in version of quem that the current beta is using and I can't do host pass-through at the moment.
I suspect your CPU has Hyper Threading, correct? Hyper Threading can make the issue worse, so while I don't want to say turn off HT, but maybe run a test with it off and see if that improves the situation. The VM is not aware of HT and treats all cores as full CPUs and does not schedule threads properly. I believe you can tell the VM the actual CPU topology (X Cores X Threads) but I never dug too deep into it. I suspect if I did it :right" I'd see some improvement in DPI latency, but I'm at a point that works for me.
Below are a few of the threads that helped me get to a playable state. Before doing all this games would studder very badly and was unplayable and for me this system was indented for game streaming, PLEX, backing up physical systems and a number of other minor functions.