Using the faster cards may give you little or no performance boost depending on how you use the camera. For the D100 and similar cameras, there is a frame buffer that can hold up to 6 shots depending on the image size and quality selected. The speed of the CF card only determines how fast that buffer will clear out. Even with the fastest CF cards you can fill the frame buffer many times faster than you can clear it out. What the faster CF cards will buy you is a slightly faster recycle time. If you do a lot of shooting in continuous frames mode, you might find faster memory useful to "re-arm" the camera for another series of frames quicker. On the other hand, if you are a macro or landscape shooter who typically takes one frame at a time, you will never realize the benefits of a faster CF card. I am in the latter category, and as a result purchase the cheapest CF cards. Even with such a card, I can fire off 3-6 continuous shots every 30 seconds or so, suitable enough to shoot hummingbirds feeding at a feeder, for example.
CF cards are at least as resistant as (or more so than) low-speed film to X-rays. I shoot both film and digital, and don't worry too much about it either way. It's easier to pocket CF cards than 20 rolls of film, though.