IGT-20 and IGT-21 provides dual microSD slots and supports up to SDHC. Read/Write test has been performed with the default 8GB MLC microSD. Here’s the methodology and test result:

Reading the microSD

root@igt20:~# hdparm -tT /dev/mmcblk0
/dev/mmcblk0:
Timing cached reads: 474 MB in 2.00 seconds = 237.00 MB/sec
Timing buffered disk reads: 62 MB in 3.07 seconds = 20.21 MB/sec

Writing the microSD

root@igt20:~# dd if=/dev/zero of=/media/512M bs=512M count=1
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 48.1249 s, 11.2 MB/s

Update: The result is just for reference, for the SD cards might change anyway.