Yes,
I did not save the region images but wrote down the values. I am talking about VR images, but guess this will be the case with "normal" images as well.
-the whole image 13K: 3% noise level equals 25 passes.
-region (small part approx 1200x1200 pixels):
5% noise level equals around 250 passes
4% noise level equals around 400 passes
3,6% noise levels equals around 560 passes