A core is a core... whatever is running on the core will be affected by the down-clocking. It's not possible for a single core to be operating at two different

A core is a core... whatever is running on the core will be affected by the down-clocking. It's not possible for a single core to be operating at two different speeds simultaneously. Note that a CPU can switch fairly quickly between different clock speeds. It's not instantaneous but it's pretty quick. I'd encourage CPU pinning if you can (pinning each VM to a specific core). If you're depending on oversubscribing, that won't be possible, but presumably you'd already be expecting more of an impact from noisy neighbours anyway.