If you want a lot of detail about CF cards and how they interact with your camera, go to this link:
Not only is this a performance database, it does into some good details about CF.
I know nothing about the Canon A70. Here is my guess. You won't see any difference between the 24X and the 25x. Heck, I'd be surprised if you saw a difference with a 12-15x. Only the really high end cameras can take advantage of the really fast cards....
I know nothing about those brands you listed. Since I don't know lots about CF brands, I'd take that with a grain of salt. Personally, I'd consider mail ordering a CF as you'll have a wider selection and better prices (usually.)