Billion 7800 vs Speedtouch 546 v6

Been having a battle between the above routers on my LLU line for streaming quality on the TBB speedtest. They are both tweaked to 1.5db giving a sync of around 18 meg. The Billion is flagged up as having streaming problems by the TBB speedtester but so is the Speedtouch but less exaggerated.

The billion will drop to zero once per TBBx1 test and ramp very quickly back up, but the speedtouch will only drop a little then burst over the average line. This is repeatable on my new Xilo LLU line.

Anyone else on ADSL2+ see this with their router? Most video streams are in bursts so its not noticeable unless the video requires a constant solid stream.