Somehow I doubt the nh-u12p cools better then the V10. Remember that the V10 has a Peltier in it. It might cool better then the V8 however.
Seeing as the V10 has a Peltier, only get it if you have a beefy PSU. Peltiers suck a lot of juice, so when its turned on, your PSU load will go up quite a bit. And Micky is right, before grabbing a V8, make sure there isn't a better/smaller cooler out there.