The cores start to throttle at 70C, which is far hotter than even the hottest garage.
Thermal dissipation however is proportional to delta-T (change in temperature).
A 25C ambient will provide delta-T of 45C, but a 35C ambient will provide a delta-T of 35C: so your 35C ambient garage will reduce performance by at least 22% compared to 25C.
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Note that Intel chips can go all the way to 95C or 100C, making cooling a far easier problem. So you're already dealing with a lower Delta-T when you use these AMD chips that throttle at 70C. (To be fair: AMD and Intel's measurement systems are a bit different, so we can't compare them directly. But IIRC, most people have a slightly easier time cooling Intel chips).
AMD spent the extra few $ for a good thermal connection between the silicon and the heat spreader.
The new threadripper and Epyc chips are also physically quite large. It's much easier to cool the head spreader with 8 hot spots spread across the chip than a single smaller hot spot.
So generally it's easy to get 180 watts out of a threadripper/Epyc chips than the equivalent Intel. In fact some of the highest end chips are not considered feasible to cool on air. It's either water cooling of throttling, like in the new Intel based Frontera (don't confuse that with the AMD based Frontier cluster).
Basically keeping a dual socket Xeon 8280 cool without throttling is not practical on air.