Here are my latest results of the SD card test. Using a Sandisk SDHC Ultra Plus! 16Gb. Smallest card I could fine!

SD Card Test
------------
SD card is connected :-)
Card type is SDHC
File system space is 15923.15 Mbytes.
SD library is able to access the filesystem

Reading SDTEST1.WAV:
Overall speed = 1.31 Mbyte/sec
Worst block time = 0.77 ms
26.54% of audio frame time

Reading SDTEST1.WAV & SDTEST2.WAV:
Overall speed = 1.30 Mbyte/sec
Worst block time = 1.56 ms
53.84% of audio frame time

Reading SDTEST1.WAV & SDTEST2.WAV staggered:
Overall speed = 1.30 Mbyte/sec
Worst block time = 1.18 ms
40.84% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV:
Overall speed = 1.08 Mbyte/sec
Worst block time = 7.00 ms
241.10% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV staggered:
Overall speed = 1.08 Mbyte/sec
Worst block time = 2.05 ms
70.69% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV, SDTEST4.WAV:
Overall speed = 1.00 Mbyte/sec
Worst block time = 3.58 ms
123.32% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV, SDTEST4.WAV staggered:
Overall speed = 1.00 Mbyte/sec
Worst block time = 2.45 ms
84.55% of audio frame time



Much better performance!