My parents have been having speed problems with their SH1 since a little while, I've also posted on the official VM forum (from their connection) but I can't work theirs out. The TBB graphs have good days - when everything is perfectly normal - and bad days, when it's not. An example of days when both happens..
The stupidity is, when TBB is reporting massive issues they can have decent speeds - maybe not the full 100Mb/s but pretty close. Then when TBB is perfect, they only get 5Mb/s or so. Wired vs wireless makes no difference save for topping out at 70Mb/s, put the wireless next to the hub, no change. All very odd, and it doesn't fit the usual pattern of congestion either.