I debated this as well. I went with 44” x 64” so I could still pull a car into the garage 
it’s been perfectly sufficient for me thus far and I really like the way the feet of the QCW sit almost directly over top of the steel Kreg frame. I was toying with the idea of attaching the QCW directly to the Kreg bench, but since I have the secure from beneath version, I wanted to maintain access to the bottom of the machine by tilting it up, as shown in the manual.
All that said, Jim is right. If you have the space, why not go bigger?
Also, are you aware of the fixed leg stand from 1F? Pretty killer deal for something that’s purpose built for the machine. I do personally think it needs some additional support (cross members between angled legs at a minimum), but that’d be easier to brace than building a table. I went Kreg before this was available and had submitted a feature request for it. They listen to us 