Hi Jonathan,
Are you saying that the images are all equally noisy at all the settings? Or that you cannot see any difference between the settings??
I use the same camera and in low light situations (if this is what you are doing) and my experience, you are going to get some noise whatever you do. So I leave noise reduction off all the time and never use it and if the image is noisy, I use Nik to clean things up, or if it is mainly colour noise, then I use the colour noise reduction in ACR first and then Nik.
Photobloke