Queued(Multicore) Rendering - This will boost your in-game performance in most cases up to double the frame rate. Currently the option is hidden and you will have to enable it manually every time in order to use it, this is in case there are still problems with it.

Instructions on how to enable it are below
To enable Queued(Multicore) Rendering, enter the following console commands into your console before entering a game.

gmod_mcore_test 1
mat_queue_mode -1
cl_threaded_bone_setup 1

Link Source: http://psteamcommunity.yuanyoumao.com/games/garrysmod/announcements/detail/877456033724316107