Thanks for all the tips!
For those of you who would not invest in a rig now: What would you do with the money in the crypto scene?
At this point in the cycle I agree that it is NOT time to be thinking of buying a new rig. Two main reasons for this is the currently highly inflated price of the components due to all the new people getting in, and the insanely high difficulties to mine any of the coins due to this inrush. As has been pointed out, ROI times of 12+ months are assured and may never make it as you are trying to pay down a rig you paid 1.5x the price for compared to 6 months ago. Relying on reselling your cards will also be a gamble as once the masses realize the jig is up, there will be a mad dash for the exits and mining cards will flood the secondhand market.
The main argument I hear for buying a rig now is that "if ETH goes back to $400 everything will be great again". This is wrong as it does not take in account the difficulty increase in mining. When the run-up first began early this year, one of my rigs could make almost 1 ETH per day by itself. Now it takes almost 20 rigs to bring in that 1 ETH per day.
So even with ETH returning to the $400 range, profits will not be as great as they were and the difficulty is still climbing day by day. It will take a month or two of very low to negative profits before people start abandoning mining in mass due to them clinging to this hope that if price recovers everything will be ok again. The price would need to not only recover but grow exponentially again (think $800, $1200, $1600, etc.) for daily profits to keep up with the growing hashrates being added daily.
Getting to your question, the thing to do now and in the immediate future would be to take that cash and invest directly into the coin(s) you would otherwise mine. I think both BTC and Ethereum, as well as many other coins, will be trading pretty low here just before August 1st. You might even pick up ETH for $150 or less in short order. For sake of comparison lets look at some examples.
You invest say $6,000 in a new rig (using your specifications from above). You would build a rig capable of making $15-$20/day after electrical costs. This would take you 400 days or well over a year just to recoup your investment. Even if the coins were to double in value again you would only be looking at $30/day or 200 days to ROI. But these values do not count the increasing difficultly, so again it would probably be closer to 2 years, if ever, to fully ROI.
Take that same $6,000 and buy ETH. Say it does go down to $150 you could buy 40 of them. Even if ETH recovers to "just" $300, your $6,000 becomes $12,000, or double your original investment. So the question you need to ask is what is the more likely outcome in the next two years. ETH recovering to at least $300, or mining to remain profitable enough to just break even, much less double your investment?
Finally I just used ETH as an example, you would probably mine Equihash (Zcash) or some other algo with Nvidia, but the overall principle is the same as all coins are following the same downward trend in mining profitability.