I'm going to try a couple other fan assisted cooling options, as I'd like to keep the setup reasonably compact.

I just ran fiber to my desk and I have a more expensive QNAP unit that does 10G SFP+, but this will let me max out the connection to my NAS.

Although I managed to panic the kernel a couple of times without the extra heatsinks on...

I think, tragically, the blog post has caused this price increase.

The offers on Amazon are most likely all drop shippers trying to gauge a price that works for them.

You might have better luck ordering directly from China for a fraction of the price: https://detail.1688.com/offer/836680468489.html

What also may not work are Dell rNDC cards. They look like they have OCP 2.0 type 1 connectors, but may not quite fit (please correct me if I'm wrong). They do however have a nice cooling solution, which could be retrofitted to one of the OCP 2.0 cards.

I've also ordered a Chelsio T6225-OCP cards out of curiosity. These should fit in the PX adapter but require a 3rd-party driver on macOS (which then supports jumbo frames, etc.)

What also fits physically is a Broadcom BCM957304M3040C, but there are no drivers on macOS, and I couldn't get the firmware updated on Linux either.

Spec for reference, I’m not 100% sure. https://docs.nvidia.com/nvidia-connectx-5-ethernet-adapter-c...

In my experience, the cheap eBay MLX cards are DellEMC/HPE/etc OEM cards. However I also encountered zero problems cross-flashing those cards back to generic Mellanox firmware. I'm running several of those cross-flashed CX-4 Lx cards going on six or seven years now and they've been totally bulletproof.