On my 147, it will happily sit in 5th at 30! 1,500 rpm, cruise along, don't accelerate in 5th from 30 tho, this will make the engine struggle and ruin the mpg... change down to 4th and accelerate, then back into 5th and cruise along at new speed. If you don't believe me watch the "current mpg" figure, putting it into 5th any earlier than 30 or accelerating causes it to drop massively, however just sitting in 5th at 1500rpm it reports 45 -50 as current mpg!
I get 27 - 30 average mpg round town, which rises to around 35 if there's a lot of 40 zones where I can leave it in 5th.
On a journey, doing *speed* I can get anywhere from 30 - 34.
On a run doing 56mph (most efficicent motorway speed in any car) I get around 36 - 39mpg.