If the QB-9 loses out to the C5, it's a possibility that the computer system wasn't fully performing.
I'm not saying that it wasn't - but it is a possibility.
It took awhile before I got my MBP and QB-9 to move beyond the C5's performance.
It wasn't the equipment in my case, it was the learning curve that I had to climb.
So I am not sure they can be directly compared as there are so many variables - it's not simply one or the other - at least it wasn't for me.