What do you recommend ?
And do you know the H/s of the 7970ghz/280x on zCash ?
1) Go to whattomine.com.
2a) 7970/280x 24-30 MH/S on dagger-hashimoto (ethash) algo, just don't mine eth/etc with it. It also dual mines pretty well, just don't mine eth/etc with it.
2b) 7970/280x 300+ on equihash algo.
3) Do your math.
4) Do not mine eth/etc with it.