After many tests and analyse about Handbrake's files, here what I get with what I think it's best setting ratio quality/weight for Youtube. Note that quality is enought for art like painting. The key value for QP is 27.
So here is my EPR file to find these settings in Premiere. It must be placed in your folder:
Windows: C:\Users\UserName\Documents\Adobe\Adobe Media Encoder\12.0\Presets
Mac: Documents/Adobe/Adobe Media Encoder/12.0/Presets
Note that you need a GTX 16x0 or a RTX card, otherwise file will be approximately 2.5 times larger (The reason is the availability of B-frames) that is almost the same size than with H264.
A sample, I get a 207MB file for a 4mn17s video HD1080 at 25fps :
and the original file from Voukoder uploaded to Youtube : https://fromsmash.com/tIhB3eaAMN-ct (available for one week)
Thanks for your feedback if you think there is still room for improvement