The 690 is a very .. very old card already .. and I didn't buy it for crypto mining but rendering.
My point is that it sux that my old card has after so much time till more cuda cores than any new you can buy.
And the Titan Z.. well ..who in the right mind will buy that one!? I wonder if they every sell one such card for the price they dream. So forget about that one.
The 690 was in the price range of a normal card back then.
uhhh... you can not compare maxwell cuda cores vs kepler cuda cores.
"Nvidia claims a 128 CUDA core SMM has 90% of the performance of a 192 CUDA core SMX" see
http://web.archive.org/web/20140221105651/http://anandtech.com/show/7764/the-nvidia-geforce-gtx-750-ti-and-gtx-750-review-maxwell/3So 128 maxwell cores are equal to roughly 0.9*192 = 172.8 kepler cores.
now while you still can not not compare the two architectures on just cores, we can at least try:
gtx 690
cuda cores: 3072 (kepler)
gtx 980
cuda cores: 2560 (maxwell) which is roughly 2560 * (172.8/128) = 3456 (kepler)