Hi Cringer.
I too owned a Yellow Mille, but mine was the R version, which should not make any difference.
From April 08 to November 09 I travelled 17,342 miles and used 1824 litres of standard unleaded fuel, giving me 43.21 MpG.
My journey was from Hastings, East Sussex to Mayfair, Central London. As my daily 133 mile commute used most of my tank, I had to fill up at the same place every day, and the average tanks varied from 30.99 MpG to 52.86 MpG (this latest one was purely motorway, without the Central London bit.
A great deal depends of your riding style, and not necessarily speed, considering these beauties are difficult to resist. The phenomenal growl of the Akrapovic can is one of the most addictive sounds I have been exposed to.
When I had to let myne go, my neighbours actually stated that the twin roar is actually a pleasant sound, despite the poor souls having to listen to it at the kind of hours that could land you with an ASBO.
And one more point, keep your tyre pressure checked to the appropriate levels, which if memory serves me well, should be 36 front and 42 rear, but it has been a while. I think the pressure is printed on the chassis, by the chain.
Enjoy your ride, I still grin thinking about it, but remember that the more miles you ride, the higher the odds that something could happen. Stay safe.