It is established that Bootcamp Partitions running in VMware or Parallels would be slower then a true virtual machine.
How slow?
I don't know. I know there is a slight noticeable difference, especially with Suspend, Resume and opening of Applications.
Is it slow enough that you'll want to throw the system out of the window?
No, It's not that slow, but there is a difference. Day and Night? Nope. More like slight gray and white.