I'm happy to answer whatever questions you have about Aubracs ... I wasn't trying to hijack your thread. If you'd rather discuss offline or privately rather than gunk up this thread, feel free to do so. Since I don't know much about mini Herefords, I didn't offer anything on that part of your idea.
So -- Aubracs do great on grass; the US breeders use the phrase "Grassfed Greatness" to try to summarize a long list of positive traits into an easy to remember phrase ... the French breeders say "one calf, per cow, per year" ... both are applicable. It's not uncommon to have cows well into their teens or early 20s calving annually on a forage-only system. I have four 12 year-old halfbloods I'm using for recips and two others who are over 10 (both of whom I'm hoping to flush later this year). Longevity and fertility are well-established breed traits.
Regarding "decent butchering weight" ... some guys butcher right off the cows at 6-9 months ... others grow them out for their own freezers for as long as 3-4 years. I do a bit of both --- I'll have some 'young beef', and will also butcher steers at 12-18 months, 2-3 years, and 4+ years ... some of my buyers like more flavor and others more tenderness. To give a sense of size, mature fullblood cows are 1200-1300 pounds or so on average and in average condition and mature bulls would be 1800-2500 pounds ... each would have an average framescore of 5.0.
Regarding the advantages of an Aubrac cowherd, they are the #1 of all Fench breeds for calving ease. This is particularly noteworthy since the majority of Aubrac cows are bred in a terminal cross program with double-muscled Charolais bulls for a very highly regarded branded beef program (Fleur d'Aubrac). They have high butterfat content milk (research indicates it's around 4.2%, which is comparable to Brown Swiss as 4.0%, Guernsey at 4.5%, Hostein/Fresien at 2.6-3.5%, Jerseys at 4.9% and milking Shorthorns at 3.8% -- I got this data
here for the other breeds).
Regarding their ability to handle extreme winter weather -- the two largest purebred Aubrac-based herds in North America are in Montana. They hair-up well, are not afraid to shove the snow aside, and are very (!) feed efficient. Each guy can put whatever amount of stock they want in this, but, just yesterday I spoke with a rep from Igenity; he pulled the data out of their system and told me that the average of all Aubracs in the system for "relative feed intake" was 4.6 and the average for all Black Angus in the database is 6.6 (lower numbers mean more efficient) -- meaning the average Aubrac will consume 0.9 fewer pounds of feed per day to achieve the same average daily gain as the average Angus. The guy with the second largest Aubrac herd in the US also runs a large commercial Angus operation; the Aubracs are his key to reducing his input costs.
Regarding their ability to handle extreme summer weather -- due to their coloring, their internal body temperatures are lower in the hottest parts of the day ... my experience with these cattle have shown the darkest-furred animals of other breeds hiding in the shade while these are grazing when it's really hot/humid.
Below is a picture of our best cow -- not a great picture, but you get a sense for what she's all about. Her name is Violet and she's 8yrs old here, early in the 2nd trimester. Deep body, wedge shape, and very feminine.
The bull below is Maximus -- he was sired by the same bull as Violet, and their mothers are full sisters. He is the most well-known Aubrac bull calved out in the US. He's swimming around in our semen tank right now. Deep body, well-defined musculature, and very masculine. Sexual differentiation is high in this breed.