You're only ever going to get indicative results with this type of testing as you can't ever perform a 'fair' test.
My own opinion is that if the Billion performs better (higher sync and/ or throughput) and is more/ as stable in use, how many errors it records in operation compared to the HG612 is irrelevant.
Service: Talk & Surf 100
Modem/ router: Billion BiPac 7800N
Target SNRM: 3.3dB or 52% of ISP
Current sync: 9755kbps
FTTC cab in place but not enabled..... yet!