It does depend on the camera being used. Some certainly can and do make use
of the faster write facility, but it does tend to be expensive/pro ones
that do.

If your digital camera has a video mode at a high-ish resolution (say
640x480), you need about 12x plus just to keep up with the frame rate for
data being dumped to the card.

Essentially, just thickness. CF type I is quite thin - II is thicker. Some
cameras cannot accept the thicker CFII cards.

I and my family own three digital cameras, an Olympus E20 (Dad), E10
(Mum) and a Canon D10 (mine). Both Mum and Dad use ordinary CF type 2
cards and I use a Lexar 512mB 32X in the D10. When we put the Lexar
card in the Olympus cameras, we notice no difference in write and
retreval speeds, but when we put ordinary cards in the Canon, things
get slower. I suspect that this has a lot to do with the camera's
processor and buffer speeds as opposed to the architecture of the chip
in the CF card. More modern cameras such as the Canon have higher
processing speeds and larger buffers and hence write / retrieval
speeds which outstrip the ability of the slower cards, whereas the
higher speed cards in older tpes are limited by the ability of the
camera's processing speed.

So, if you are considering a modern digital camera, the higher speed
cards may be of benefit, even more so if the camera has a large cache
memory or large buffer, whereas older cameras tend to write and
retrieve at a rate which higer speed cards can't capitalise on.

CF type 1 cards are thinner than the more modern CF2 cards and
generally have lower capacities.

Perhaps a high speed card may not be such an improvement on a slower
processing camera.

Just a hunch base on personal observation.

Richard

just a hunch, based on personal experience.