Yeah, I'd say it's pretty good! I have it installed on top of my 6700K @ 4.7 and couldn't be happier with the temps ( well, truthfully I'd be happier with an NH-D14/15 or Cryorig R1). Highest temperatures I've seen while playing Witcher 3 were:
core 0: 59
core 1: 62
core 2: 58
core 3: 58
Highest temps with FSX after flying through ORBX FTX Pacific Northwest near KSEA area for about 2 hours with every slider at MAX even though at times fps dipped down to about 10 fps (because I really wanted to try and stress the cpu) were:
core 0: 62
core 1: 68
core 2: 62
core 3: 60
I was thinking that the Intel style tabs would not be able to hold the cooler down, but they're actually holding the cooler really well on top of the cpu. I still don't trust them though. Installation was nerve-racking to say the least. I was worried that I would waste a lot of what little AS5 I have left. The push-pin tabs kept moving out of place very easily with the slightest movement, but I managed to seat the cooler on my first try.
It's very noisy because I'm using 2 coolermaster sickleflow 120's in push-pull, but I love it nonetheless. It's actually doing a better job than the H75 that it replaced. My 212 Evo runs just a few degrees cooler than the GAMMAX 400, but in testing the 400 out, I lost track of where I put the 212 plastic fan holders and ended up breaking all 4 of them by sitting on them. I COULD use the metal fan holders for the 400 on the 212 but I don't like how easily they can slide off of the 212 cooling fins.