Comparing Compact Flash Card types

I'm shopping for a high capacity (512MB or 1 gig) for my new canon S1
IS, (I want to use its 640x480 movie capability, necessitating high
capacity). I see a few types on the market, I'm asking for info from
those that have experience or knowledge. I'm leaving brand name
considerations out, so as not to muddy the issue. So far, it looks
like the only significant difference between type I and type II is
the physical size; so if I get a type II it won't fit in my old canon
SD110. No biggy, really, I've resigned myself to get a type II. The S1
IS takes either one. So my concern is that I believe that taking
movies may REQUIRE a 'high speed' CF card, and the best I can deduce
is that the regular type will write maybe 6MB/sec, 'ultra' will write
at 9MB/sec, the 'extreme' claims 16MB/sec, but also has inernal
recovery s/w if the card fails.
A 512Mb CF card, roughly, goes for: regular type II, 100-125$. Ultra
type II, 175$. Extreme type II, 250$ !!!
Obviously, I'd rather not spend more money for speed I don't need, I
would think there's a memory buffer in the camera that acts as a
reservoir while it's filming, writing to the flash card as the flash
card can take it. But if there's any risk at all that the card is the
week point, I'm willing to spend the extra money for the 'ultra'. The
'extreme' sounds nice, but as we all know from the great 'steve's
review' (and others) site, there is third party recovery s/w available
to recover images from a failed card, so I'm dubious about the feature
of internal recovery s/w.
Please, talk to me!
thanks so much,
Rick