Newegg has an HD 7870 for $170, it is rate as mining at 375 khash. The 7950 is pretty much the same as 7970 for mining and cost $430 giving roughly 700 khash. Thus 2.2 khash per $ vs 1.6 khash per $.
I am considering buying 2 7870s for $340 and using them in my computer in sli mobo which works fine for mining. However most people are buying 7950s and r9 280x and 290x which is what has jacked up the price, this the reason I'm considering an option almost 100 cheaper giving 50 more in khash.
What do you recommend?
Honestly, its all about scalability and what you can afford now. Sure, you'd be saving money in the short term, but if you plan on building a rig, what is it going to look like then? Are you going to wait until then to spring for 7950s/7970s? If so, what are you going to do with your 7870s? You'd definitely lose money in resale value.
Also, you might want to consider power draw, as that should factor into your calculations. 7870s are approximately around 200W per card, one 7970 is approximately 300W. You'd be using more electricity. Can your current power supply handle that? What would the extra cost look like?
