@Stan, great! If you use an SD, I highly recommend using the SdFat Library running in configuration zero (uses DMA). In that mode it will write at 3-4MB/s!
As for the FRAM, you will need to serialize your data in a byte array that you can DMA out. That should be easy to do using a join within a data struct so you store your captured data in a uint16_t array (0-4095) but DMA it out as a (union) array of uint8_t.