Because the HTC Desire has a very small NAND I decide to buy a fast Transcend 16GB Class 10 SDHC to run APPS2SD or DATA2SD hacks.
Test tool: SD Card Tester
Old speed (Samsung Micro SDHC Class2 4GB)
Write: 300MB at 2.26MB/s
Read: 301MB at 7.53MB/s
New speed (Transcend Micro SDHC Class10 16GB)
Write: 300MB at 7.46MB/s
Read: 301MB at 9.8MB/s