Good answers, thanks, especially since the larger more common size would likely be in stock more often. The DuraGuard from AC-Delco and the Purolator filters I like always seem to be out of stock at my two closest auto-parts stores so this is good news for me.
One more question... I always add six quarts exactly to both my 4.0L and my wife's 4.7L engines. I thought that both of the owner's manuals say six quarts is what they hold. Am I overfilling them with six quarts? It seems like the dipstick always says they're exactly full after filling them with six quarts.
And Robert, there's no reason not to go to a larger filter, I was just curious why a larger filter was such a good thing... especially since without this thread I wouldn't have even known which larger filters would fit.