SuperAdithya :
dovah-chan :
titan black > 290X
More compute power, more VRAM, runs cooler, etc. overall just better ^^"
But, there is more clock speed in the R9 290X!
Clock speed is NOT important when comparing different GPUs. If you were looking at two different R9 290X models, then clock speed matters. But when comparing a R9 280 vs a GTX Titan Z, its not something you want to take into account. Different GPUs use different clockspeeds. Faster clockspeed doesn't mean faster GPU (unless they are the same, as I said with the 290x vs 290x).
http://www.anandtech.com/bench/product/1186?vs=1059
I would say the R9 290x is a little slower, but as usual, it comes down to which programs/games you will be using... Have you considered an R9 295X2 or a duel GTX 780 ti setup?
R9 290x if you don't mind a minor performance loss for $500 savings, Titanz for the extra performance boost.