So, as of the latest nightlies, we support:
Someone should punish Haiku to see what kind of data transfer numbers you can generate 
In theory, NVMe’s, plus two systems chatting over a 10 Gigabit connection, should be able to transfer data at 3.5GB/s+
If you can figure out how to do a RAID 0 of the NVMe’s (Haiku doesn’t have software raid at the moment) and present it as one physical NVMe… that is ~6.0GB/s in theory.
Just saw your post! O.o which Ethernet card do you have exactly I’m thinking of putting on in my system… and don’t want to buy something risky that might not work… I remember you got a model with SPF so you could swap transcievers if you wanted but I don’t remember the exact model?
My stress test would amp it up a bit with 256GB ram and 32 opteron cores 
I do also have an NVMe card (m.2 to PCIe adapter)… but I have to pick and choose which slots I have enabled as they don’t all work at the same time… so we’ll have to see if I can do a PCI sound card + NVMe + 10GBe. Note I only have PCIe 2.0 so I am slightly bandwidth limited compared to modern NVMe cards.
I wish I could throw my Vega FE in the mix too but… no support for that sort of stuff yet.
Emulex OCE11102 Works great, only $14 on ebay.