Changed Graphics Cards - Saved Money ?

I switched graphic cards in my home machine from a 8800 GTS to a GTX 660. The difference was an astounding 70W (measured) during idle! With current energy prices, the new card pays for itself in about ... 5 years.  Which is about the usage time of the old card.

In terms of the mathematics, was this now the optimal time to change cards, given the pricepoint and the wattage and availablity of this card at this point in time ?