Truthfully I wouldn't bother upgrading to a GF4MX card at all. They aren't really worth the money you spend on them, hunt around for a cheap GF3 or even better wait a while and save some more cash, the price of the Ti series will be dropping soon and the Ti4400 is about to be discontinued. Check out Ebay for some good bargains.
Folding for Beyond3D
"A lie gets halfway around the world before the truth has a chance to get its pants on."
Sir Winston Churchill
"Halflife2 got halfway around the world before Gabe had a chance to get his pants on."