Electronic – Are there limitations on stacking Boosterpacks for the TI Launchpads

Oh, duh, I didn't read your code carefully -- your send SendLcdByte is wrong:

    void SendLcdByte( unsigned char command_0_or_data_1, unsigned char command)
{
    SendLcdUpperNibble( command_0_or_data_1, command);
    // send the lower nibble next
 // AS WRITTEN:
    P1OUT = (command & 0x0F) | (P1OUT & 0xF0);
 // SHOULD BE:
    P1OUT = ((command & 0x0F) << 4) | (P1OUT & 0xF0);
    Strobe( command_0_or_data_1);
}

Smaller capacity SD cards will often perform better for single-block writes, because their erase page size is smaller. When you write to the card, even if you only write a single byte, the card's internal controller may have to read an entire page (often 4K) into a buffer, modify your one byte, erase the Flash page, then write the whole thing back to the Flash memory. So cards with a smaller erase page size will have less of a penalty for small writes at random addresses.

What microcontroller are you using? SdFatLab works on AVRs and does support multiple block read/write operations. Your files must be in contiguous blocks on the SD card to take advantage of it.

Check out some of the discussion and benchmarks at http://elm-chan.org/docs/mmc/mmc_e.html