Best sub-$1000 GPU setup

So I've been exploring my GPU options for the build I'm planning. I have between $800 - $900 in the budget for this. It seems there are quite a few options available for this price range and I'm curious what will give the best performance and longevity. Should I get a single 780, two 770s(4gb), two 7970s, or a single 7990? If I get the a higher-end single card I'll leave the option open for a pretty awesome sli setup down the road, or two cards will provide me better overall performance in the short-term (thinking dual 4gb 770s). 

Some relevant information: 

I'll be playing at 1440p

I won't be building/purchasing until late August. 

I'll be building with a i7, and z87 probably.(Relevant? I'm not sure)

  1. The 7990 will stop having support soon as they will be more concered with the newer gen.
  2. Two 7970 ? If your going to wait for the new drivers to fix the CF issue
  3. Money not a issue for you then get the 780
  4. I would wait for AMD to release the newer Gen and see what they are packing

Triple 7950s will be the 'best' in terms of performance.

AMDs new line should be out around late August, the 8xxx series.  Any information you collect now will be irrelevent then.

I would throw the 7950 into your list of considerations. It is like 3% slower than the 7970. So dual 7950s would be more than enough performance at 1440p, more than a 780, if I am honest. It's a low cost option. I happen to like the '50 more than the '70. I don't think the '70 has sufficient performance to warrant the extra cost.

You've said previously that you wouldn't be building this rig for a few months? I might be wrong. So, Brent has made a good point that new cards could be along in that time. AMD is actually skipping to the 9000 series. And they have a card which competes with the 780, apparently.