Ah... If you read the page that you gave... even bishop doesn't guarantee it will work 100% on every win8 machine.
Yes, it can. You can even install Win95 on it :D
Slow down? It depends on your host's spec and how you set the guest OS.
A dual core is plenty (just use XP and set 1 core and 1 GB ram)
but it's recommended using a quad core for win7 guest OS (set 1-2 cores and 1-2GB RAM depends on the lag on guest OS), although you may try on a dual core system if you want.
It's something like a delete and forget thing incase you don't like it.