What's more important GPU cores or GPU memory?
I would not bother buying new hardware to mine low rate. I suggest you try mining with your existing hw. You could try cpu-mining MAGI, it's easy to start with: https://bitcointalk.org/index.php?topic=735170.0

You won't strike it rich but its a nice mining start.

If you want bitcoins to use anonymous I suggest you find someone local to buy from with cash, or buy a prefilled creditcard and use that to buy coins. 

Mining pools don't pay for your hw specs, they pay for the amount of work contributed.