I'm not so sure this is the proper section for your question, but I'll do my best to give you the little bit of knowledge I have on the subject. I've just recently got into mining myself, so I'm not a wealth of information. For about $600 it seems like you might be overspending on a card like the 1070 for mining. I got two 1080ti's for $1400 total, or about $700 each. Granted, I bought them from a vendor around here, but they are very trusted with not a single negative review in sight. They took very good care of their cards and I do not expect their previous usage to have a significant impact on their lifespan/performance. I plan to ROI in just a couple months, but my main point is that it seems like if you look for your cards a little harder you could get a lot more bang for your buck.
https://bitcointalk.org/index.php?board=160.0 - Altcoin Mining section, might be better served to look for information there.
Also, I have a 980ti that I would be willing to sell for pretty cheap, definitely will help clear up some room in your budget while maintaining good power, it has seen very minimal usage. If you're interested in saving a couple hundred bucks on one of your card slots and buying it from me for your rig, let me know.