Nice, I wish I had seen this before I wrote my own library, although I needed the goldelox SGC command set.
I did implement all of the SD card functions in the 4D command reference (my thread is at the bottom of the first page ATM) but I didn't really find anything unusual about them compared with any of the rest of the commands. The only one that needed any special handling was ReadSector, for which I found I needed to increase the Rx buffer to be much larger or else I would lose 75% of the block (which in turn would cause my version of nacAck() to lock forever, so I added a simple timeout to prevent the worst case).