Better MPG

You can't beat D-Jet with MegaSquirt on a stock B20E, you're using the same injectors, so where is the fuel saved?
D-Jet can't adjust on the fly, it's only as good as the last tweaking you did to it. Lots of humidity, and it's running rich. FPR acting up a little? Who knows, rich or lean. All in all, running a motor lean is generally bad, without O2 feedback in D-Jet you need to be a little more conservative and run it a little richer just to be on the safe side. With O2 sensor feedback you can run it leaner and still be safe. Use a wideband sensor and you don't even have to tune to stochio, as a NB sensor pretty much confines you to.

AFR's held closer to stochio for cleaner burning

I don't see any point to that?

Run it much leaner for more MPG, or richer for more power, stoichiometric is for looking after your cat.
Generally, running much richer isn't good for it, running it leaner with a crude overall adjustment like you'd get out of a D-Jet tweak, and you'll hurt it from high cylinder temps at WOT.


SU's are hard to beat on fuel economy too, but they give up some power & torque due to the manifold being poor.
Seriously? Take you average old SU equipped car, and you'll find it running pretty poorly, getting poor MPG. Maybe if you hand tweak them seasonally, with a great deal of skill, you could do OK. But if SU's were really better, they'd still be using them.
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)