Here is a comparison video about SD cards write speed tests on Sony a9 II and a9. From the result, we can see that Sony a9 II is much faster than a9 in 5 second burst:
Test 1: Use Single Sony SF-G Tough UHS-II Card (B&H/Adorama/Amazon)
- Sony a9 – 34.56 Seconds – 102 files
- Sony a9 II – 21.32 Seconds – 102 files
Test 2: Use Dual Sony SF-G Tough UHS-II Card
- Sony a9 – 34.13 Seconds – 100 files
- Sony a9 II – 26.25 Seconds – 103 files
Test 3: Use Single Sony SF-G UHS-II Card
- Sony a9 – 28.53 Seconds – 100 files
- Sony a9 II – 21.63 Seconds – 102 files
Test 4: Use Single Sony SF-M UHS-II Card (Amazon/B&H/Adorama)
- Sony a9 – 40.77 Seconds – 103 files
- Sony a9 II – 33.69 Seconds – 103 files