Well the more quiet one i'd assume would be the H70 as it is water-cooling. Also the better cooling would be the H70 as the H50 performed very well with the push-pull config, however if you were going to compare the two, I wouldn't pick the NH-U12P SE2 as the H70 is practically 30-40$ more than the NH-U12P if you wanted to compare it i'd pick the NH-D14.
Which actually looking at it, the H70 would actually be louder (26-36dBa) while the NH-D14 or the NH-U12P SE2 (19dBa with ULNA) So the quieter is the NH-series while the better performing but way more expensive is the H70. The NH-D14 though is quite frankly the most powerful aircooling available. So it could put a good fight.
Also based on this review for pro H70, Although it states the better performance, the CM Hyper 212+ is only 25$ vs a 110$ cooler Not to mention the 212+ hasn't been given great fans in dual fan config, which still would put you at a much cheaper price (the Hyper 212+ is cheaper on amazon rather than Newegg)
The H50 was only as good as top end air coolers when you put noisy fans on it. As for the H70 I have read some people saying its only as good as the H50 and others saying 10C+ improvement (which must be exaggerated) a majority said it was only a very slight improvement over the H50. I would recommend getting a high end air cooler with some high CFM fans and a speed controller so you can balance the noise & cooling how you like.
From what i've read i think it's fair to say the H70 provides better cooling then any air-cooler but that will cost you in noise the fans produce.
The H50 is quieter but is outperformed by the top air coolers.
The one bonus you have is low profile ram that won't cause any mounting issues if you decided to go with a high-end air cooler.
The best air-coolers available are the Thermalright Silver Arrow(an improved version of the Cogage Arrow) and the new HR-02 and Venomous X,Noctua NH-D14,Prolimatech Super Mega/Megahalems(discountinued)/Armageddon.
I finally found the review i've been looking for Battle of the Big Boys. http://www.vortez.co.uk/contentteller/articles_pages/th...
To answer your question the H50 is even superior to the Noctua NH-U12P SE2.
And i agree with aznshinobi a CM Hyper 212+ will do a great job it's very hard not to mention it when talking cpu coolers.
There is no "Brand" on the stock heatsink for thermal paste, it's just stock thermal paste. Easy as that, all you need to know is that IC7 or MX-2/MX-3 would perform much better. Some use AS5 but those are usually aftermarket heatsinks that use that as there pre-applied compound.
I'm facing a similar predicament. Stick with the corsair H50 or go with a noctua nh-d14 which is due to be delivered this week.
My main concern is coolant leakage. While the risk is low, the risk is there. With the noctua nh-d14, if the fans fail, I'll will not kill all of the components like if the H50 dies (leaking liquid + electronics = )
Given the performance of both coolers, are nearly the same, I'm leaning towards the monster DH-14 as opposed to the small H50