I am not sure why you are concerned about your purchase.
I don't think the Nocturas fair badly...
Looking at the <19dba lines:
Noctua NF-S12-1200 5V <19dBA 640RPM 18CFM
Noctua NF-S12-800 9V <19dBA 660RPM 18CFM
Scythe Kama Flow 7V <19dBA 610RPM 16CFM
Scythe S-Flex 9V <19dBA 620RPM 16CFM
Nexus 120mm 7V <19dBA 680RPM 19CFM
It doesn't seem the others move any more air when running silently.
I cleaned up your lines to match the format I use, now I'll add a few more:
Slipstream SH 1900 7V 18dBA 630RPM 21CFM
Slipstream H 1600 5V 21dBA 890RPM 30CFM
Slipstream M 1200 5V 18dBA 720RPM 24CFM
Slipstream M 1200 4V <18dBA 620RPM 20CFM
Slipstream L 800 9V 18dBA 640RPM 21CFM
Slipstream SL 500 12V <18dBA 440RPM 14CFM
Now the H 1600 can't get slow enough to really compete with the first list.
Also the SL 500 doesn't do enough CFM to compete either.
But the M 1200 at 5v or 4v beats any fan on the either list for noise to CFM ratios as far as I can see.
Surprisingly the SH 1900 can be undervolted enough to also best most of those fans.
And the L 800 makes it to the list as better than average.
But then all of this data wasn't available to us before this week so there is little reason to beat yourself up over it. Just take note and buy the better fan next time (fans don't last forever).
btw the data is from Fan Roundup #5
: Attack of the 120 Scythes