Welcome to the forum Bleevin. Do you have a budget in mind? Is your space already finished or are you building? Are your ceiling standard 8 foot height?
Personally, I would go with a 7.1 setup with that kind of space. The difference between 5.1 and 7.1 isn't huge, but there is a difference - how much can depend on the room. also, it looks like there's a lot of open connected area, so without knowing all of your relevant details I would tend to go with larger speakers (M60/80) with a good subwoofer to make sure you get good 'room filling' sound. The real experts will be along shortly - I'm just a hack at this stuff having a good time along the way!
Cheers,
