mget_temp was reading up to 82C on one of the cards. I mounted a 120mm fan above them and the temperature dropped to 52C (actually still dropping as I type this).Correct answer!
In a 3U/4U chassis where you cannot easily duct airflow just mount a side fan that blows onto the card. That is sufficient. You don't even need a fast spinning fan. I do the same in my Fractal Design Define case to cool a ConnectX-3 card.
I wish knew about the cooling requirements of these 10G nics when I bought them. Spent unnecessary time debugging issues with my setup.
Not sure how I can cool with the space allotted. The chip clearly seems to be the hottest issuedon't underestimate the cooling needed by the transceivers.