I’ve got very tight clearance behind my servers. I was wondering if one type of SFP+ module is shorter than the others. If it wasn’t for the space issue, I’d use DAC ‘cause it’s just between servers. But every inch more the servers stick out is one inch closer to me walking into them… 
That situation sucks, but if you don’t have enough space behind your servers for a DAC then you don’t have room for proper fiber bending radius, and for adequate server ventilation.
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There will be enough space for ventilation.
The difference in latency doesn’t matter in my application so it’s just a matter of which is less susceptible to damage by distracted me bumping into them. And it seems DAC is the answer. 
Edit:
The rack is a foot from the wall. I’m clumsy. The less anything sticks out the safer it is from being damaged by me. I’d rather not move it out any further because then it would encroach into the three feet wide path to my furnace required by the fire code.
Most modules are the same length. To prevent crush, attach wood to the back of the rack so it can only be pushed so far back, then you don’t need to worry.
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