Basically if you got a Tahiti you are better off mining XMR at the moment.
Reason why is because those you can reduce the voltage to the min value of 0.950V and if you got a decent ASIC quality you can run them at 1000/1500 core and you will get like 600H/s and it will only use like 130 Watts of power.
With ZEC it always used almost 200 Watts or so. With ETH it used even more electricity. The worst was Scrypt which was like 350 Watts per GPU from the wall.
its not that crazy thing is its not about the instant profit witch if i did mine xmr it would take me a year to get one lol.
its about the stacking and holding and right now btcz is the best for this using my cards on old algo i was getting close to 1000 a day on my two 7970s and 4930k that would just be doing nothing otherwise.
dnt care about imediate profit thats what my asics are for.