Shameless self promotion, but I think this might actually interest some here.
Card temp without: 70+++°C
Card temp with: 56°C @ 30% fan.
Only adds 2-3mm to the width of the card, final width is still well within 1 slot.
Printed in 2 pieces, no supports, PETG works. Should fit most (all?) 100GbE CX4 and CX6 cards.
Yes, it’s soviet-ugly but I’m not Johnny Ive. It does work well though. BOM & models here:
https://www.printables.com/model/997890-mellanox-connectx-cx-4-cx-6-active-cooler
Step file included: it should be straightforward to adapt it to whatever enterprise card you got off ebay, be that a NIC or a HBA or whatever. 
