I get average 27 MPG in my 2003 Sonata that is rated for 25 highway, I get over 70 average from my DT rated at 69 highway. I get 27 highway from my Sorento SX V6 AWD rated at 24 highway. What does getting over raed mean, you drive to get MPG!
As stated engine temps are regulated by the thermostat, now it were air cooled and all else were equal that may be different. As far as race engines, they arew meant to be rebuilt to maintain peak performance. Som drag engines are rebuilt per run etc.
To replace/supliment grease or heay oil I can see where the teflon addative can have some use. For modern engines that like even 0-5 weight oils the addative is probably more a hinderance than help.
As far as stories of well maintained engines etc, there exist many even without addatives. Ususally however those looking to use these tend to otherwise take care of their engines as far as schedules maintenance and therefore naturally will have longer lasting components. Again though it is your money.
Now for a test I would take to heart they need an engine with a known oiling issue. Such as run sets of 5 dodge 2.7 V6 engines (known oil and sludge issues) with one set on dino, one set dino with adative, another set on a good synthetic and lastly a set with the same synthetic and addative. run all to failure with proper maintenance and then pull them all apart. Now of course all would have to experience loads and accelerations etc. to simulate real world application................