Hate to burst your bubble, but I doubt a $900 budget will be running those at ultra, unless we're talking under 60 FPS, maybe even under 30. And what'll be more important? CAD or gaming? CAD is CPU intensive from the 30 seconds of research I did. Games lean more on GPUs.
Here is a good reference guide for choosing your parts based on different budgets. http://www.hardware-revolution.com/best-mainstream-gaming-pc-march-2014/