Meh, This is fact's and i think you should go for either 290x (depends on the budget) or 290. Here are some fun facts:
R9 290X (to the left) 780TI (to the right)
Higher clock speed 1,000 MHz vs 875 MHz Around 15% higher clock speed
More memory 4,096 MB vs 3,072 MB Around 35% more memory
Higher pixel rate 64 GPixel/s vs 52.5 GPixel/s More than 20% higher pixel rate
Better floating-point performance 5,632 GFLOPS vs 5,040 GFLOPS More than 10% better floating-point performance
More render output processors 64 vs 48 16 more render output processors
Wider memory bus 512 bit vs 384 bit Around 35% wider memory bus
However, let's look at 780 TI's reasons why to buy.
780 TI(on the left) R9 290X (to the right)
Better passmark score 8,676 vs 6,622 More than 30% better passmark score
Significantly higher effective memory clock speed 7,000 MHz vs 5,000 MHz 40% higher effective memory clock speed
Better 3DMark vantage graphics score 44,390 vs 40,400 Around 10% better 3DMark vantage graphics score
Higher texture rate 210 GTexel/s vs 176 GTexel/s Around 20% higher texture rate
More texture mapping units 240 vs 176 64 more texture mapping units
Significantly higher memory clock speed 1,752 MHz vs 1,250 MHz More than 40% higher memory clock speed
Significantly better passmark direct compute score 4,781 vs 3,349 Around 45% better passmark direct compute score
Better civilization 5 texture decomposition (2013) score 396 vs 373.9 More than 5% better civilization 5 texture decomposition (2013) score
Lower TDP 250W vs 300W More than 15% lower TDP
If you sum this up, it means that 780 TI gives you more fps and performance, it scores better. But with new drivers i think that R9 290x wont be very far away, AND if you calculate how much this cost, the 290/290X wins epicly.