It seems to me like it's quieter.
No, actually they shouldn't be quieter: the Slipstreams are nearly identical to the Nexus ones, maybe even a bit quieter (running 50-100rpm less at 5V, while giving the same about 13 CFM, even if I dunno about relevant static pressures).
Yes I concur, they are both good fans.
It would seem that, generally, from the testing results attained by SPCR over time, that it is likely the Nexus has better static pressure than the slipstream... but this is wild guesswork/extrapolation on my part.
The slipstreams clear advantage over the Nexus is that they downvolt easily to 5 volts. The Nexus can't do that.
At 13 CFM, static pressure is not much of a factor... the airflow is more like drifting air than a stream of air. It is like that aerodynamic efficiency of a car - very important at 120 miles per hour - but much less so at 12 miles per hour.