Using the convertProfit function (http://zorro-trader.com/manual/en/pip.htm) I get only one tenth of the normal value as PIPCost for the SPX500.
Comparing SPX500 to US30, while they have the same PIPCost (when convertProfit is not used) US30 has about 10 times the RollOver cost so the convertProfit-PIPCost seems to be the correct value.
However, the PIPCost FXCM lists on its website (http://docs.fxcorporate.com/user-guide/ug-cfd-product-guide-ltd-de.pdf) is the normal value, which is kind of strange.