IIRC the max TC in 3d view setting controls the tc setting above which fatigue doesn't change. this setting may influence other things as well

So if you have your max 3d TC set to 1024, then at this TC there is possibly a lot more happening than if you had left the max 3d Tc set to default.

High TC will bring a fast cpu to its knees, particuarly near a harbour with lots of ships. Rendering stuff in 3d AND updating the game world at high TC is just too much... ubi undoubtably found this, and thats why they put this setting in.

I have an athlon 2000+, and near harbours the game (on map view) becomes a slideshow for me at anything more than 128x