With the DOW down 416 points in one day we should be able to see the PPT in action. In fact, we may have already seen them in action with a large sell off of metals and mining stocks. This sell-off actually preceded the loss on the DOW but is rather counter-intuitive. Instability of stock markets and currency increases demand for gold. So perhaps this sell off (liquidation) was a way of stemming the tide before the bad news of China really hit?
If China does indeed hit a large slump that could mean some interesting times in commodities. Uncertainties would increase the cost of precious metals but may well drop the cost of base metals. That is assuming that any slump would significantly slow down development. And a slump in the Chinese currency could actually benefit the US with even cheaper imports, but that is assuming that corporations would pass along any savings to consumers which isn't too likely.
Despite the 4% drop in gold, it is still far outperforming stocks and has been for years now.