I thought the 6000 was slightly lower throughput than 5090, but obviously has a shitload more RAM.
There's two models that go by 6000, the RTX Pro 6000 (Blackwell) is the one that's currently relevant.
A40 nvlink was limited though, one-to-one (bridge), never saw it daisy-chained or nvswitched (might have just not seen them myself, they may have existed).