Sandisk 4GB Extreme III or Ultra II Compact Flash Card

I'm thinking of buying a 4G card. I have a Canon 350 and will buy a better body in the near future. The price between the Extreme III and Ultra II is about $25. Is there any practical difference between the two? I do not often shoot continuously and when I do, the number of frames is small and probably will fit within the camera buffer. What do most people use?