[jpgvm]

Plus in a modern DC you can trivially convert it to be essentially lossless with DCSP/PFC and ECN which both work perfectly with any UDP based protocol (and is why NVMeOF, FCoE and RoCEv2 all woke so well today).

ECN isn't a necessity unless you need truly lossless network but the rest should get you pretty far as long as you are reasonably careful about communication patterns and blocking ratio of spine/core.

For anything that really needs the lowest possible latency at the cost of all other considerations there is still always Infiniband.