Um, why are you even running screen savers in any virtual machine?
Obviously they aren't going to save the "screen" from burning in an
image. They don't save power. And the screen saver you are using for
your host OS is what gives you the lockout security for your host.
If you are, say, allowing remote access to the VMs and are somehow
thinking that a screen saver provides security, why are you wasting CPU
cycles running a screen saver that has to compute an ever-changing
screen? Just use the black screen saver. It runs at the same speed all
the time: just a black screen all the time.
During the VM's bootup and hitting Del to go into its BIOS, you will see
there are no settings for changing the clock or multiplier on the CPU.