VirtualBox is OK for trying out new OS's w/o risk, but it's not quite like the real deal. Remember those anti-Windows 8 You Tube videos? Many were using VBox for those propaganda videos, making Windows 8 CP & RP look poorly, to turn users against 8. Looking at some of the videos closely revealed this.
I have dual boot, & I also have 4 working computers, so actually I can have Windows 8 & Zorin OS on at the same time, in real life speed. Plus on my main two computers, I have SSD's (a 180GB Intel 330 & 128GB M4), so all of that fast boot gimmick stuff isn't needed. I have Windows 8 Pro on two computers, one a "fast boot", on a WD RE4 & the other on the Intel 330, it's pointless to state which is the fastest.
However, I've yet to try dual boot Windows 8 & Zorin OS, now I have a reason to, to see which boots fastest on the same hardware. That in itself doesn't make either better than the other, though. Thing is, all one has to do is place their OS in hibernation, which is what is happening with 8, & see which is the fastest. It may or may not be Windows 8 that's truly the fastest starter.