OK, mods over. I have decided, slightly reluctantly, to trade in Helga for another car. I'll come to the reasons in a moment.
I have entered the final fuel log for Helga which is based on an estimate from the SG2. I added 5% to the expected fill-up volume reported by the SG2 which is 1.5% over the usual error I have been getting tank to tank - I chose 5% as it is a nice round number and I am lazy
Including that though the last tank is the best as it would be, and the trend would suggest Hypermiler status in maybe 2-3 tanks.
So why the change ?
Ultimately I just fancy a change, but also it is down to costs. At the moment I am paying ~£300 a year in insurance (Helga is a high-ish group being a sporty girl) plus £135 a year in tax. I am currently refueling every 5-6 weeks which means that those costs are now very significant - i.e. its not just fuel any more. The £135 tax will pay for 3 tanks, or roughly 2 months of fuel. The insurance would pay for 4-5 months.
I would do without and when I worked in the centre of town I considered not having a car at all, however now I work outside of the city I do need a car, public transport doesn't do it and I can't bike as I also do kid runs to and from school. And based on my posts on education it looks like I may have to think about private schools for A-Junior - annoying though that is.
The final tipping point was an offer which included "6 months free fuel" - it is not quite that simple, it is not for a period but it is an amount - £500 which is put onto a fuel card as part of the deal. I won't use this amount of fuel but it is based on the card not the car so Mrs A can take that card and use it against her mileage in the Prius.
The replacement ? It is a Toyota Aygo "Go" like this one :
Even the same colour.
From enquiries with owners it seems the best a normal non-hypermiler can do is ~60-65MPG so I hope to better that. The other cost are roughly £150 a year for insurance and £20 a year in tax which is about 4 months of fuel at my limited usage. These add up to £260 a year straight away which pays for a fairly large part of the trade in cost alone.
The Aygo does not have the, er, 'go' of Helga though. I will miss the thrust in the back when the turbo kicks in and the ability to match some very exotic machinery - the motorway trip back from England at 11pm pacing a Bentley Coupe at 120+ using it as my radar detector will be a wonderful memory. (note to any police reading, this didn't happen...)
But I just don't drive that way any more. I rarely venture over the limit anywhere. On the motorway (limit 70) I am more likely to be at 60 or even 55 cruising with trucks to get FE. I coast a lot, engine on, and rarely overtake. I drive like my Grandad did in his Morris Minor.
So this is the last post for me on mods in the this thread, I'll maybe look at tyre pressures and some limited aero in for the new car when it arrives, and also technique which from experience with Helga is the biggest single factor. The Aygo is designed with lightness built in (~850kg vs. a Yaris at 1200kg) which will help in the urban driving I mostly do.
And I have to think of a name for the Go for the fuel log - suggestions welcome