Did some troubleshooting and found a base game bug?
The mod menu uses more CPU the more mods are enabled. It doesn't matter what the mods are or what load order. As soon as you click the x to a checkmark it starts using more CPU and once you have a lot of mods loaded the mod menu eats your CPU. You don't even have to restart the client to see this in action. Just start enabling mods and watch the CPU usage climb.
The mod menu uses more CPU the more mods are enabled. It doesn't matter what the mods are or what load order. As soon as you click the x to a checkmark it starts using more CPU and once you have a lot of mods loaded the mod menu eats your CPU. You don't even have to restart the client to see this in action. Just start enabling mods and watch the CPU usage climb.