well, if the price drops for 20% or more and I own some antminer s7, the difficulty will either not rise so much or will decline, s3 and s4 have to go offline soon in that case. The buying price of the s7 is also not really affected.
S7 will mine in profit zone as long as there is no newer (more efficient) hardware.
Price drops -> resell value not (so much) affected, difficulty may rise slower
Price rises -> resell value not (so much) affected, diff will rise faster but price will compensate some of that
So it's not so important if the price goes up or down with real miners. Price goes down and you mine more BTC (in comparison to price rise). Price goes up and you mine less coins but they are valued more.
Price drops -> you spend xxx USD and get less back. Period.
Price rises -> same as buying BTC and hoping for stable or rising BTC/USD
I would say, the risk of PACMIC is way higher than buying s7 shares. PACMIC is pure BTC/USD speculation while the S7 will never consume more than it generates until new hardware is available.
If the price goes up, you win with both options, but if the price goes down, you will definitely lose on PACMIC.
To back my claim, that if price goes down -> less hashrate increase: