I noticed a drop in performance with one of my larger worlds in the 2018 beta. The world uses local VRC_Triggers for culling in a lot of places with OnEnterTrigger/OnExitTrigger so I made a test world to see if VRC_Triggers had a higher performance overhead in 2018.
The test world has 16,384 VRC_Triggers that have no events assigned https://vrchat.com/home/world/wrld_96b53d10-b32f-4d78-bbc9-895f4cd0c888. In 2017 I am able to maintain 90 fps with the 16k trigger objects enabled. In the 2018 beta I get 35 fps once I toggle on the triggers. I turned the trigger count up to 35k on live and still didn't drop below 90 fps. 35k was the largest number of triggers I could make before I started timing out while loading into the world.