I'm talking mostly abour scaling things like app servers where they might not need any communication.
But in general if you can't scale horizontally at 10 gbps, you're in for a world of hurt. Numa gets you to 8x scale at best on very expensive very exotic hardware. And then you hit the wall.
And single socket is equally cheap, except it takes twice the rack space - but it also gives you redundancy. One server can fail and you can carry on.
The advantage of memory bandwidth vs Ethernet for scaling to x2 really doesn't matter. If it did, you're not horizontally scalable and at best you buy a little time before you hit the wall.
If the price difference isn't much, I would heavily prefer single socket.
But in general if you can't scale horizontally at 10 gbps, you're in for a world of hurt. Numa gets you to 8x scale at best on very expensive very exotic hardware. And then you hit the wall.