Originally posted by glanglois As you note, class 6 is the fastest standard, at only 6 Mbps. The EIII cards are rated at 20 MB/s so it would be something like a class 20 and 133X. There is no class 20 so no class would or should be indicated on the packaging. They certainly don't want an unwary buyer thinking that their very fast EIII cards perform the same as someone else's class 6 at only one third of the speed of the EIII.
And this is why I get a bit aggravated when class six cards (at only 6 MB/s) are marketed as very high speed, fast as they get, etc. They are, at best, in the mid-range. Even the Ultra II at about 9 MB/s is 50% faster than class six.
The standards body for SD is working on those faster standards and we should, I think, see one or more of them this year. But that work may be no more than documenting the technology that's been shipping for quite a while now.
Yes, of course you are right, Sandisk does claim a
minimum write speed of 20MB/s for Extreme III, I didn't notice this until now. (Although see below, reviews show it to be not quite that fast.) And "20MB/s" meets (and exceeds) the specs for for the fastest class, so it is labeled Class (6) although it is much faster.
Based on claimed minimum write speeds, we could conclude:
1. K200D (5.5MB/s) could benefit from the write speed of any Class (6) card (6MB/s), but not from any card that further exceeds Class (6).
2. K-m (10MB/s) can benefit somewhat from a the Extreme III (20MB/s) compared to an Ultra II (9MB/s). Difference should be +11% faster (=10/9).
However, that may not be the case:
Here is a
review of a number of SDHC cards. The
conclusion is interesting:
"...we found substantial performance differences of up to 100% in the write throughput benchmarks, where the cards delivered between 9 and 18.6 MB/s. And the speed classification didn’t help much, as some Class 4 cards delivered better write performance than some Class 6 products."
While the Extreme III is judged to be the best of the test group (along with the Lexar Professional) it's minimum write speed is only measured to be ~13MB/s, which is 35% slower than SanDisk's claim. They didn't test the Ultra II but extrapolating the data we could assume that the Ultra II also under performs compared to the claimed minimum write speed of 9MB/s.
So we could revise the second point of our conclusion:
2. K-m (10MB/s) can benefit somewhat
more from a the Extreme III (
~13MB/s) compared to an Ultra II (
~6+MB/s). Difference should be
up to 67% faster (
=10/6).
Looking forward to your test results!!