Everything that is present to oxidize and lead to stale beer post-fermentation is present at mashing-in. Given that reaction rates double for every 10°C increase in temperature, your wort can oxidize over 100x faster at mash, boil, and cooling and transfer temperatures than beer at fermentation and storage temperature. So everything you can do to mitigate the effects of oxygen on the pre-fermentation side will produce a fresher tasting wort. Rigorous exclusion of oxygen from the moment of pitching until the beer hits the glass will preserve flavor as long as possible; it's a question of what initial product you're preserving. Hence the low-oxygen brewhouse technology implemented by the Germans in the last 50 years to extend shelf life of their fragile export Pilsners, which are nonetheless skunked to undrinkability even before their green bottles leave the filling line.... Many measures are being taken by homebrewers, including use of antioxidants and adsorbants forbidden by German custom, and their effects have experimentally been shown to be even more significant at the homebrew level, probably because of relative surface area exposure and other scale effects. Again, it's not all or nothing, or any one thing, it's cumulative effect. And +1 on reducing thermal stress, that may be the best bang for the buck.