CAD and Matlab are going to be very CPU-intensive. I bogged down my i7-930 trying to do extensive Matlab calculations (it ran at 100% usage and ate up 2-3GB RAM). I would recommend a quad core minimum if you do some really intense stuff with that, or your computer is not going to be very speedy while running that stuff.
Yes, get this mobo and quad core processor:
mobo: ASUS M4A89GTD PRO/USB3 AM3 AMD 890GX HDMI SATA 6Gb/s USB 3.0 ATX AMD Motherboard ( has got all the new feature and can do CF if you need to.)
CPU: AMD Phenom II X4 955 Black Edition Deneb 3.2GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Quad-Core Processor HDZ955FBGMBOX
( just enough for gaming and easy for overclockin, you get what you pay fro with this cpu)
Ram: G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL7D-4GBRM ( due to it's cas latency been 7 it's good) the lower the cas latency the better.
and a gurd quality PSU like corsair or antec or somethink like that