A few other things to bare in mind, if you choose to stick with your SD shield(s) and use it with other SPI peripherals. With the exception of the Seeedstudio v4 reader and MAYBE the Itead (I have not tested this board myself), you will run into issues due to the lack of a tri-state / Hi-Z buffer on MISO line (if I recall correctly). This means that an SD card's MISO output will interfere with other SPI peripherals that share an MISO line. Due to the nature of how SD cards are controlled via SPI, I would strongly discourage the sharing of SPI lines between and SD card and any other SPI device in general.
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