These files lower the lodDist values in the nwvegetation ymap file. You should see a significant increase in performance.

Paste the nwvegetation file of your choice into mods\update\x64\dlcpacks\northwoods\dlc.rpf\x64\levels\gta5\northwoods.rpf\  

Some extra tips for performance:
- Turn off MSAA
- Lower Distance and Advanced distance scaling settings