Updated weight mod for v1.11 

Download the "witcher 3 weight mod.rar" and unpack it.

Put the files from "Witcher 3 weight mod" folder that you unpacked into the following folder:

[installation drive]:\The Witcher 3 - Wild Hunt\content\content0\bundles

Run the 9999.bat file.

After this, load your game. Drop a item on the ground

1) press i for inventory
2) select item you want to drop
3) press r to drop it
4) pick it up

Inventory is refreshed and you will have 9999 weight without any slowdown anymore.
credits go GiecuMan and sup2069