This falls into the “I might rent a small car on holiday (or maybe, even, drive all the way there in the Mini) and I’d prefer to know beforehand” category.
On long mountain road descents, normal speeds: 40-70mph, do small 3-cylinder engines provide sufficient resistance in 5th/6th to help stop brakes from cooking? Never driven down anything severe/long enough to find out.
Please excuse ignorance. Longest hills near me are done after 1.5 mins max.