EDIT: A did a little reading on the Catholic Encyclopedia, hoping there was some garing obvious answer, but sadly, there isn't. After a surprisingly extensive explanation of the omniscient/free will problem (you'd think they would hide that somewhere) they ended with this:
"Whichever way we turn we are bound ultimately to encounter a mystery, and, when there is a question of choosing between a theory which refers the mystery to God Himself and one which only saves the truth of human freedom by making free-will itself a mystery, most theologians naturally prefer the former alternative."
Oy.

Something I've thought myself: If it comes down to it, I'm choosing God over free will. Free will seems like an illusion to many athiests and psychologists, anyway.