I just purchased a new 4GB Sandisk (class 2) SDHC card and wanted to share some interesting test results... As someone might remember I do have two tablets and I also have 8GB Patriot Class 4 card that I purchased a while back. I did some comparison testing of write and read speed on them on different slots, different firmware (patched and non-patched) and in different N800 units.

First of all, it seem "Sandisk feature" that it does not want to operate in high speed (48MHz) mode. It reverts back to 24MHz bus speed on my patched N800. While this was slightly disappointing... it doesn't appear to be as bad as it sounds... read on...

I didn't use the dd or any other "built in' speed test, but I used a 319MB video file in my PC that I wrote to N800 and read back to PC using USB cable. I timed the time to transfer with a stopwatch. Both cards were formatted to a single FAT32 partition using 2k block size.

Test results with N800 having patched kernel:
Card: Ext/Int: Write_time: Read_time:
8GB E 188s 25s
4GB I 132s 43s
8GB I 185s 25s
4GB E 135s 42s

And here are the results of N800 having non-patched kernel. (The firmware is the one that is planned to be released next Tuesday... )
Card: Ext/Int: Write_time: Read_time:
8GB E 195s 40s
4GB I 132s 42s

I didn't swap the cards in the slots on the second unit, since it didn't make any difference in the results (excluding error margin) on the first unit... Just being lazy there...

So, the findings. Surprisingly the Sandisk Class 2 card outperform the Class 4 Patriot card in write speed!!! Based on the dmesg logs it is running at 24MHz speed. So, in other words, the bus clock speed is not that important as I was thinking it was... Likely the memory card timings play a big(ger) role.

The high speed mode seem to help only on read speed.

And, as if you interpreted the results of my second tablet, you can make educated guess if the new firmware will support high speed mode...

Oh, and last, both cards have identical write speed (60 seconds to write 319MB file) when used with an external SDHC USB reader/writer. So the N800 is still very slow when compared to a dedicated reader/writer... Anyone planning to do a lot of file transfers to/from your memory cards, I highly recommend to purchase external reader/writer.

UPDATE:
I just rerun the test when using external USB reader. It seems that the memory card speed gets slower when there is more data in it? After some 400MB worth of MaemoMapper files are stored on the card, the write took 66 seconds, and the read back took 31 seconds. The same test on the Patriot 8GB Class4 card (having approximately the same amount of data) took 60 seconds to write and 20 seconds to read.