I've nver had the Zalman but I've used both the rev1 & rev2 Nv Silencer 5's on my GT. With the stock cooler, my temps were around 59c idle/78c load. I put the rev1 one on and promptly broke one of the crappy screws (idled @ around 65c for about a week until i got my rev2). The rev 2 is on now and I idle @ around 49c and top out @ about 65c. I'm pretty happy with these temps -plus my case temps went down 4 degrees cos of the exhaust on the cooler. I would def recommend the nv5 but just make sure you get the rev2 cos I've heard of lots of people having problems with broken screw threads