Regarding the speed test results, I've also noticed the ThinkBroadband test seems to show much lower single thread speeds on Virgin Media compared to other single threads tests. This has been going on for a couple of months, previously it was very accurate.
Here is an example taken within the last few minutes:
55Mb / Burst 69Mb
DSLreports set to a single thread:
Test file downloads from ThinkBroadband always reach the speeds reported by dslreports and testmy.net, it's just the ThinkBroadband test which seems to report much lower single thread download speeds.