I suggest you make a NG virtual machine creation a part of installer progress and not after installation, so users know the high CPU usage is the result of avast! installation and not a bug. I mean, if they see a high CPU usage and the installer says "Creating virtual machine installation" or something along those lines with note "CPU usage may remain high for a few minutes", they will be assured it's fine and all part of a normal installation process. But if CPU is getting hammered later on, they will think it's a problem.
You could also use a popup that would reassure users that high CPU usage is a normal thing for the duration of NG installation. I know it will be run at lower priority in RTM, but i think it would still be smart to let users know what's going on. So they don't panic unnecessarily.