from memory, I upped the MWay speed to 80.
not because I go that fast, but I found that it made it more likely to use them that way
Mind - this was on day 1, when I was trying to work out why it wanted me to divert through the middle of Newport to get to Bristol from Cardiff...
(was before I'd RTFM and the route settings had been set to 'avoid MWays'
)
then never got round to changing the speeds back...