We we here in Georgia are located RIGHT SLAP in "tornado alley." I have seen three with my own eyes. One of them tore the roof of my old house. That's the one storm I am frightened of.
As for the shifter knob, I have several suggestions. You could see if a friend with a C5 will let you take his off and see if it fits yours. Our C4's come off VERY easily! You could go to take yours off and take it to a dealer and see if they have any in stock for a replacement for a C5, or you could just buy it outright and hope it fits and wait till you DO have a C5! :L
I think I would take it to a dealer to the parts dept and compare or see if he'll let you try to fit it on your C4. But taking one of it REALLY easy. First take a small, thin bladed common screwdriver, then you need to get some snap ring pliers with different points as the holes in this snap ring are small. Carefully remove the snap ring, making sure it doesn't fly off somewhere in the car! Pull the knob up and see some rust on the shifter! You can still drive it, just gotta push down on a metal shaft now. Lemme know.
Paul