First ever build: AMD vs Intel for Gaming +olater CAD use

I am trying to figure out what would be a better option for me. This is my first self-built computer, and hoping for it to last a while. I'm on a budget (<$1000 if possible) but looking to set up a fairly powerful system.

It will be primarily used for gaming, but in a year or two MAY (not for sure) start getting some CAD use as well as Finite Elements and Mathematica.

First thing first, AMD or Intel.
I've been looking at i5 2500k vs. Phenom IIx4 965/970
Phenom x6 1100T I have Also looked at some.
The i7's seem to push me out of my price range fast.

With that, what GPU would likely pair best with the CPU you see most fit. Not really planning on going dual card anytime soon, if ever, most things I've read so far sudgest it really isn't worth it.

And if you're bored, pair a motherboard?

In terms of hardware, I'm near illiterate, but reading up on stuff and slowly learning. In terms of OS's themselves, I'm pretty proficient (triple booted my macbook last year   )

Thanks for the help!