Personally I've never been tempted to try anything like this, based on the fact that a) I'd rather work things out for myself, and b) I'm hurtling towards Old-git-dom at a frightening rate of knots and therefore anything that smacks of new technology is obviously the spawn of Satan. [Cries of: "Get back to 1974 yer silly old sod"]
One thing that became obvious from the late '90s onward is that engines were being optimised in pretty much the same way, either that or the gearing was almost identical.
For instance, the fish-faced Fiesta 1.25 Ghias I had around that time were geared in such a way that 2,000 rpm in each gear corresponded to 10, 20, 30, 40 and 50 mph. Subsequent 1.6 Focuses (Focii?) were the same. Even my Panda MJ has the same speeds in gear. A noticeable exception being my 156 2.0 litre TS which is quite short geared, so much so that it pulls about 500 rpm more at 70 than the Panda.
The other aspect is that most diesels now produce maximum torque at around 1,800 rpm, and the curve is then pretty flat until about 3,500.
Much of this is down to engine management systems which mean petrol cars are quite often as tractable as a diesel used to be. In fact the gear change indicator on our Giulietta Multiair 170 keeps on telling me to change up at around 1,500 revs.
Personally, around town I try and change up at around the 2,000 mark on the Panda, Giulietta and the Zafira I use at work. Mind you, that's an example of the gap between older and newer engines as the 1.7 in the Vauxhall can trace its ancestry right back to the first of the FWD Cavaliers. It's as flat as a three day old pint of dark mild until it gets to the aforementioned 1,800 revs whereupon it starts picking up and then goes berserk until about 3K when the engine decides its had enough and takes its ball home.
As for mpg, although these aren't exactly direct comparisons, the Giulietta seems to be getting high 30s on mostly urban commutes and low 40s on motorway runs and cross country drives, but these are just estimates as I've yet to check it brim to brim. A similar car, but with a different kind of engine was a Mokka diesel I used recently. It was the 4X4 version which I presume is a part time jobbie like the 500X Cross. Using a more mature version of the Zafira's 1.7 diesel it gave me 41 mpg (worked out) which wasn't exactly what I was expecting.
Another, completely different, car I used recently was a Mercedes C220 CDi which on mixed urban, rural and motorway running gave around 35 mpg.
Methinks we're being taken for a ride by car makers when it comes to fuel consumption.
As for the MA engine, so far, leaving the DNA thingy wotsit in N and changing up at 2,000 revs as mentioned before seems to do alright. When Mrs. Beard uses it for a few weeks the trip computer thingy shows about 38mpg, when I use it for a while it shows 42 as I tend to be more disciplined (anal?) than she is. I know trip computers can be inaccurate, but 38 & 42 mpg seems about right. If I'm mooching around then 2,000 rpm it is, but if I have to go past that then I quite often block change up, for instance from 2nd to 4th.