Testing a passive / semi-passive cooler with a fan running 1000rpm and 2500rpm does not make much sense to me.
What is a NH-D51S? I have heard of NH-D15S and NH-D15, but never a NH-D51S. Assuming it is NH-D15S, why is it being tested with 2 fans? NH-D15S is sold with a single fan, not two...