Your post is, for the most part, pure nonsese. No offense.
Yes, JDM (and therefore European and Australian market) SVXs use a different tranny. But other than that the differences are pretty superficial. I've never heard anything about SVXs 'shutting down' a cylinder bank. But I
have heard reports of wildly different mileage from members on this board. Hell, my own SVX has gotten as little as 15mpg and as much as 31.
US SVXs were not 'detuned.'
I don't know about the ECUs, but I would bet that differences would only go so far as the different fuel used in parts of the world, different communication standards, etc.
If I'm wrong on any of this, somebody feel free to correct me.