As what is hopefully a final update to this thread, I had a nice speed test surprise this morning.
Pulse8 are upgrading all their customers packages, which must have resulted in the problem TTB kit being bypassed.
Hopefully all other Pulse8 users that were having single thread speed issues will see a similar improvement in their results.
Not sure whether this is Pulse8 specific or whether TTB are also moving their users over as well.
Keeping my fingers crossed that it will last.