Not sure if this is a fan or heatsink question lol.
It's a not well formed fan question, IMO.
At anyway, do you really think it would make any actual difference using a Slipstream 800rpm or an undervolted Noctua P12 running around 750-800rpm? No, it's about the same (maybe the Scythe might give some cfm more, but very few if in case).
On the contrary the Noctua have a much higher sound level at full speed, obviously.
So, if you already use a software or a rheobus to control your fans, you can evenly got your deal (I think that it should be almost the same if you run the P12 through some Noctua adapter cable).
If you want to run the fans at full speed, personally I wouldn't do so.