I say go with a gtx 770 for $350 or 290 custom for $450 and upgrade after another 1.5 years. That would be best for you.
That's essentially what I did. Bought a 680 when they first came out, got a 2nd used one about a year later. My first mGPU setup, was a bit nervous at first with some of the horror stories associated with it, but I haven't had any issues and performance has been stellar.