First, cards.

You are looking for Mellanox QDR (and FDR) adapters, preferably double port. Used, of course.

They come from supercomputers and datacenters focused on high speed storage and calculations.

Check about Infiniband kinds at https://en.wikipedia.org/wiki/InfiniBand

Cards must have QSFP+ ports, FDR are more expensive (and faster).

Mellanox ConnectX-3 VPI CX353A-FDR InfiniBand 56GbE/40GbE for $55

Mellanox ConnectX-3 MCX354A-QCBT CX354A QDR 40GbE Dual Port for $42.5

In reality last letter is bracket height - S (Short Bracket) / T(Full-Height Bracket).

http://www.mellanox.com/related-docs/user_manuals/ConnectX-3_VPI_Single_and_Dual_QSFP_Port_Adapter_Card_User_Manual.pdf

You will also need proper cable, for short distances it looks like (it is same direct soldered wires as in SFP+ case for Ethernet adapters, just more of them)

https://www.ebay.com/itm/Original-Mellanox-HP-3M-4X-DDR-QDR-QSFP-IB-Cu-Cable-498385-B23-503815-002/113404887644

For long length you need optics:

https://www.ebay.com/itm/Mellanox-MC2207310-010-10m-Infiniband-Optical-cable-QSFP-QDR-FDR10-FDR56-rate/183270585614

On software side

First, you need to check drivers availability (we'll assume that you will use Windows 10), usually it is not problem for popular Mellanox cards.

Usually rebranded cards can also work fine with Mellanox drivers.

Second, you need proper software - Windows 10 Pro for Workstations specifically, with properly enabled [RDMA] (https://en.wikipedia.org/wiki/Remote_direct_memory_access) and SMB Direct.

Without this options you will be mostly wasting your time and money (can check Linus making same error and not understanding it).

With RDMA

Without

Read about them at:

• http://wchukov.blogspot.com/2018/05/infinibandrdma-on-windows.html
• https://www.servethehome.com/custom-firmware-mellanox-oem-infiniband-rdma-windows-server-2012/

Check second link also if you need to make custom firmware (to enable RDMA!) in case your adapter is rebranded one.

Another big thing with Infiniband - it is solution to go if you plan to use Intel Optane memory as main editing drive.
With it you can do it remotely from other machine and still get amazing IOPS and keep low latency.