Good 120x25mm fans for push\pull on Dark Knight?

Nice fans or if you could get deal on 2 Yate Loon fans in med or high speed on a fan controller would be best IMO for p/p ratio. You plan to run shrouds?

Actually, slipstreams are pretty bad. They have pretty impressive airflow, but the only problem is that the motors are meant for 80mm, and they're pretty low quality.

What's your budget on fans?

Coolermaster R4 x2 would be nice:
http://www.newegg.com/Product/Produc...82E16835103061

Though I would rather just single fan it with this Panaflo:
http://www.newegg.com/Product/Produc...82E16835705003

Yep, I would also vote for the panaflo

But remember, at full speed, its going to be loud, if you don't mind the noise, then your set but if you you do, you'll need to undervolt it or get a fan controller.

I just put a R4 on my Dark Knight and it is super quiet and looks great great. I have 4 stuck sensors on my new Q9550 so I don't know how low the temps go? The lowest core is 29c at idle. I did lap my DK though.

First of all, don't go with them slipstreams, they are great as being case fans, but not for heatsinks or radiators. (Crappy static pressure) I know this from personal experience. Also the Coolermaster r4's are alright, but not great, they definitely don't put out 90 cfm, hell I think its more around 70 at max.
But the best 25mm fans in my opinion would be the Scythe GentleTyphoons, the Scythe S-Flex's, and Yate loons of course. Gentletyphoons are quiet and have great static pressure and the other two are great in their own ways (quiet with great cfm, price, performance). I say all of this from having experience with all of the fans mentioned above.