Alot of the horsepower is used for CAD work preparing things for milling on the CNC milling machine that is almost operational. I also use a fair amount for speeding up code compiles, various video processing and conversion projects, experemental audio dablings (I hesitate to call it music per say) amongst other things, etc. But one of the main focuses of this computer is gaming. I like running things in super high resolution with all detail levels enabled.
Painting a case can be a pain, but it looks cool. The amount of time it takes though almost makes it worth just getting something pre-painted inside like a CM-690 II or a Haf X or something along those lines. If you have access to a spare oven though, powder coating is also an option thats pretty inexpensive to get into.