SPI interface question
Try this.  For every 12 bits you transmit you must transmit 4 bits of overhead. So for every sample of 16 bits you must transmit 8 extra bits for a total of 24 bits per sample.  You're required to transmit 10,000 samples (per sec?) so that's 240,000 bits per second required.  You have a 300,000bps link so 240,000/300,000 = 80%.