Something I noticed about the throughput values and it kinda makes sense too: Multiples of SMM count seem to work best for the -x parameter. 5 for 750 Ti, 13 for 970, 16 for 980. Only have 750s and a 970 to test with but 20 or 15 for 750 Ti and 13 or 26 for 970 seem to work well.