Well my old Sapphire 7970 is a solid card.. It was mining way back in 2014 and it has been my faithful video game card for the past year.
I've pushed it to about broke. Without modifying the BIOS, using the factory controls, I am stable mining at 1055 core, 1425 memory. I have pushed the upper power allowance to +10% [of potential 20%]
The core clock is 950 but I have had it running stable overnight at 1125, but the difference in hash rate isn't worth the extra heat. I was good at 1500 memory, but again, after pushing the card for a few days and switching back and forth between playing a game and mining, the card has started to have video driver crashes & won't initialize unless I power off and turn off the PSU for a minute. So no more pushing it..
Anyway I settled on using "ethminer" and when I build my rig I'm going to solo mine using a local instance of geth. I was solo mining LTC in 2014 and it was the most exciting for me to find my own blocks.
For posterity, today with the current Epoch & Global Hashrate, my 7970 3GB card is getting 12Mh/s. I can push it hard to 14Mh/s. In 2015 it appears this same card was processing around 22-30Mh/s but as the difficulty has scaled up it contributes less proportionally with the problem.
I don't believe any R9 or lower cards will be economical to mine with. The Nvidia cards will be interesting, because they potentially have a much better Hashrate/TDP once Nvidia gets their shit together with their drivers. Radeon cards are better because of OpenCL, but the gap is closing.
With one card mining on a pool, and using this computer also as a gaming rig, I won't even see my first payout from the pool for months. So the danger there is you build up credit in the pool and it goes under before it pays out. Such is life in the gold rush.