I probably wouldn't worry too much about 2-3% (10% is where you should start looking at ready time) and you have Co-Stop at 0. Other than the VM showing 100% spikes were there performance issues? After adding resources do you still have any performance issues? It sounds like you are going over the NUMA boundry of 6 cores so for performance you might have issues with would be memory based rather than CPU.
https://itnext.io/vmware-vsphere-why-checking-numa-configuration-is-so-important-9764c16a7e73
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