3D cad, well I know Autodesk Acad takes forever to load on a normal hdd.
I would recommend a 256GB SSD maybe a crucial M4 or something. I don't own one yet, but have built several systems with an ssd and I wish I had one over a better cpu and video card.
Ram is cheap, and 8GB is enough, I run games, cad, etc, firefox with 100 tabs just to see how much ram it will use and I yet to break the 4GB mark.
The 560 or the radeon 6870 are both good buys.
Motherboard, I usually go asus or gigabyte, get whatever is the least expensive, but has sata 6 and usb 3.0 is nice also (make sure it is NEC chip or asmedia for a 2nd choice, entron usb3.0 still have lots of compatibility issues.)
Might want a normal HDD for some backup.
An i52500(k) would be good enough. With the i7 and expensive mobo, it will probably put a 256GB ssd out of the price range.
Life doesn't change after marriage, it changes after children!