They keep my Antec 920 liquid cooler's radiator happy, even though the MAX RPM of these is only 1500RPM vs the stock antec fans that go up to 2500-2600RPM
I found the temps on my CPU to be exactly the same as my Antec's one, at full load (this includes gaming on Battlefield 3 & running Prime 95).
Long story short:
The SP120 quiet editions cool the same amount as the antec do - however the major difference is:
-Antec's are significantly louder at full load
-Antec's go to 2500-2600RPM, whilst this "only" goes to 1500RPM, and yet provides the same amount of cooling to the CPU
So if you're looking for quiet fans, that actually do their job, at a low RPM, and compete with temps of a fan that runs almost 1000RPM faster - then these fans are the babies to go for!