CORRECTION: The RiData SDHC card is a Class 2 card, not a Class 4 as we originally reported.
Review by Gizmodo contributor Curtis Walker
SDHC, or Secure Digital High Capacity, finally lets SD break the 2GB barrier and compete with Compact Flash for capacity. Only a handful of new devices are compatible with SDHC, and there's really no support for legacy gear. This means you can't even put them into your computer's SD card slot. You need a special reader which, most cards come with. As grim as that sounds, SDHC is a welcome step-up for people who have newer DSLR's like Nikon's D80 or video recorders like Canon's high-def TX1. I entered nine of them into my own personal laptop-and-camera Battlemodo arena to determine compatibility and raw blistering speed.

Capacity is important, but so is speed. That's where the SDHC Class system comes into play. Previously, customers were presented with cards ranging from 66x to 150x, without any real guarantee of performance because there was no standard way of determining what 1x actually was. Currently, there are three classes: 2, 4 and 6, which relate directly to the minimum write speed of the card: 2 MB/s, 4 MB/s and 6 MB/s. Finally, there's an official industry standard. Unfortunately, this system only defines minimum speeds, which is good and all, but we're kinda more interested in maximum speeds. The faster the write speed of card, the quicker the shooting and transfer of images/videos off the card for editing.

The contenders:
Class 4
Delkin eFilm Pro 4GB C4 card they claim 150x speed - $60
PNY 8GB C4 card - $85
RiData Lightning Series 4GB C4 card - $50
SanDisk Ultra II 4GB C4 card with reader - $70

Class 6
ATP ProMax 4GB C6 card with included reader - $75
Dane-Elec 133 Xs 4GB C6 card - $35
Kingston 8GB C6 card with optional 15-in-1 reader - $100 and $15 respectively
Lexar Professional 133x 4GB C6 card with included reader - $100
Patriot 8GB C6 card - $75

I skipped Class 2, but as a basis for comparison, I threw in an old beater Lexar 1GB SD.

Even price turned out to be an unreliable measure of performance when put through my testing gauntlet. My street price searching found the Dane-Elec card to be the cheapest card of all, and it's a fast Class 6.

Benchmark testing:
I ran tests using each card in each of the four included SDHC readers both on a generic PC desktop and a MacBook. On the PC side, I created a 188MB folder containing 20 Nikon Raw images and timed how long it took to write the files to the card. On the MacBook, I used the benchmarking software XBench to see who had the fastest writes. (Longer is better, since we're talking bandwidth, MB/s, here. You can see how all Class 6 cards have 6 MB/s transfer speeds, but you can also see how some have maximums in the teens.)

Real world testing:
Finally, I wanted to see what difference all of this actually meant in the real world, so I loaded each card into a Nikon D80 and shot 20 raw images while timing it. The D80 can only shoot 6 raw images at full resolution before the buffer fills up, therefore the fastest card should allow for a faster 7th image, and that's exactly what I found. The RiData card took over twice as long as the fastest card, the Lexar Pro. I was especially disappointed to see that old 1GB card beat all but three of the newer hotter cards in real-world usage!

Conclusion:
The clear winner in Class 4 is the SanDisk Ultra II, which managed to perform on par with the Class 6 offerings from Kingston and PNY. That should tell you that, if you're going SDHC, go Class 6. The winner there is a close call with Lexar and ATP fighting for top spot. But when all is said and done, Lexar is King of Speed, and even though the price is a little high, the included memory card reader is a better product. If you're strapped for cash, you might look at the ATP or better still, go with the Dane-Elec card. It has no reader, so you'll have to figure that out on your own, but it does have a sweet price to performance ratio.