28C sounds fairly close to ambient temperature, so im not sure if you would get much more under that, id just stick with what you have, if anything just keeping it clean of dust, but 28C hell..thats the lowest i can get, and thats after leaving the computer sitting doing nothing, otherwise its around 30-35C which is pretty darn acceptable to me...
the shape of the tuniq looks like it has more surface area than the asus sink, so it may cool better...as well as being possibly quieter, and offering the option of changing the fan a tad bit easier... might be worth a shot if you got money laying around