Concur on #1 -- I've never been so focused as when six of us shared a large office that was isolated from the rest of the company by two doors and a set of stairs.
Similarly, a set of closed offices around a common area with couches and whiteboards. Here you get to choose; individuals can isolate, when cranking, and they can also include themselves into conversations by leaving their doors open.
Note that this is WAY different from having a set of offices along a long hallway (where you get no community at all -- hallways are just like motels, or crappy apartments).
I also concur with #1's finding (small group in a room shut off from the rest). I once worked with 5 other C++ developers all sitting at a couple fold out tables in a one room office to work on a software that was used in a highly competitive niche market and this was by far the most productive I ever was. Like the OP, we could instantly talk to one another about a problem or to ask why certain blocks of code were a certain way. We wrote software used to track bets (off shore gambling). Our software sold for around $100K and at the time (about '93-'95) our only competitor was a large corporation that appeared to struggle to keep up with us. We were so innovative and fast to deliver. Those days long behind me, I often wish to find that same cohesiveness in my work-life again.
Similarly, a set of closed offices around a common area with couches and whiteboards. Here you get to choose; individuals can isolate, when cranking, and they can also include themselves into conversations by leaving their doors open.
Note that this is WAY different from having a set of offices along a long hallway (where you get no community at all -- hallways are just like motels, or crappy apartments).