Thanks for the work on the library! Here's first results from bench for an 8 GB PNY micro class 4 in the Adafruit micro SD breakout:
Type any character to start
Free RAM: 95415
Type is FAT32
File size 5MB
Buffer size 100 bytes
Starting write test. Please wait up to a minute
Write 85.27 KB/sec
Maximum latency: 159470 usec, Minimum Latency: 15 usec, Avg Latency: 1171 usec
Starting read test. Please wait up to a minute
Read 1208.31 KB/sec
Maximum latency: 865 usec, Minimum Latency: 15 usec, Avg Latency: 81 usec
What were they thinking when they put the pins in the middle, right under the edge of the shield footprint? (I guess they were thinking minimum conductor length, and matching the original layout but not to accommodate existing shields that ignored the ICSP header...)
Here's the same card with 20 MB and 32768 Buffer at full speed.
Free RAM: 62747
Type is FAT32
File size 20MB
Buffer size 32768 bytes
Starting write test. Please wait up to a minute
Write 2074.35 KB/sec
Maximum latency: 452410 usec, Minimum Latency: 7830 usec, Avg Latency: 15788 usec
Starting read test. Please wait up to a minute
Read 4381.52 KB/sec
Maximum latency: 12166 usec, Minimum Latency: 7413 usec, Avg Latency: 7476 usec
more details at Good Things... Small Packages: uSD on the Arduino DUE including the connection system I rigged up for the Adafruit breakout board.