Stacking them? If your thinking about stacking them the output wouldn't be that much more then 1 fan, maybe 10% more airflow.
If your putting them side by side, though the vantec is a big heatsink there would be a huge overhang.
Honestly niether one of these will come close to the performance of a Delta38, could consider putting a 80mm fan ontop of it just slap it bare right on there. Or just going with a quieter 60mm fan.
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