Macbook Air w/ external display or Retina Macbook Pro?

I'm finally getting a new computer next month, but I'm having a bit of a dilemma:

I could get a Macbook Air for $1600, get an external display (found one I like for $230) and after buying a mouse and thunderbolt to HDMI cable, spend $1899.

Alternatively, I could get a Retina MBP and spend $2200.

I would mostly use it for gaming, (Minecraft, Portal 2) syncing, organizing, and downloading. I realize the Macbook Air can handle most of this, but I don't want to be stuck with a computer that's a disappointment when it comes to gaming or dealing with more intensive tasks.

What do you guys think?