Hi Petrov,
And thanks for the reply.
Yes, compared to classic jpeg files, I get slightly longer result with .tx files and more noise but it was only a test scene (just 3 x 8k textures).
For 1 frame 1080p : 5min for jpeg / 8min for tx
Dynamic memory limit : 8000
Maya 2015 & VRay 2.40.02
Regards