CPU Bottleneck

[Coldfire]

According to the task manager XIV is using all 4 of my cores

Your taskmanager is lying. Had a desktop gadget saying it uses six cores (lmao). You need a special tool to determine how many threads a program has and how much CPU-usage each thread has.

How many cores a program can use is determined by how optimized the code is for parallel processing. You basically have to extract code that can be run in parallel and fit it into a worker thread while the main thread does something else. Thanks to directX this works pretty easily for two cores as one core runs the game mechanics and the other runs the graphics stuff. This can easily be achieved using dxut or xna. If you want to use more cores you will have to split up the game mechanics(Physics, AI, Content pipeline, etc. ).