stock fans are good.
if you feel you need another one, get another Phanteks fan, they are some of the best.
this whole Static Pressure vs. Airflow discussion isn't really up to date.
a Phanteks F140SP has better static pressure than a Corsair SP140 and better airflow than a Corsair AF140 at the same time.
really high pressures are usually achieved by higher noise levels.
long story short
Phanteks, Noctua, Cougar fans if you feel the need for a nother fan.
series doesn't really matter, any will do