2x2GB for $45 is "off the value cliff." It's no-longer a mainstream "size" of memory to buy for a rig, so it is naturally over-priced per gig. 2x4GB is ~$50. [ http://pcpartpicker.com/part/gskill-memory-f312800cl9d8gbsr
Best VALUE discrete gaming GPUs for pro-apps that are accelerated through mainstream API standards (opengl, opencl, directx) are currently in the HD7750-HD7950 range for *most* apps. In some cases, competing NV cards will be competitive alternatives, but not always, depends on the specific program in question and which version standards and which features/versions those programs call on, as AMD has better version support for openCL/DirectX and a better architecture for some openCL work. Cuda is a separate proprietary issue that you will know whether or not you need.
There are some apps that do not benefit from increasing GPU power beyond a certain threshold, and limited scenarios (video editing and scientific research) that may make use of greater GPU power. As an example, Photoshop does not benefit significantly (or at all, in many cases) from GPU power beyond that of an HD7750 (roughly). Investment beyond the power of a 2GB HD7870 does not represent a good value for Autocad as price/performance drops off considerably from there on up.
Not sure how price sensitive things are with the motherboard, but I'm guessing the $80 case and high quality PSU means there's room to budge on the mobo..
Here's the mobo I would use for this sort of "ultra-boring, ultra stable, ultra long lasting desktop rig made from quality parts:" http://pcpartpicker.com/part/asus-motherboard-q87mecsm
Asus Q87 Corporate Stable Model Micro board. Yea, it's "really" boring. But rest assured this is a board that you can count on for the long haul, and count on good long term support for as well.
3 year warranty vs 1 year for the ASrock.... interesting