Does DDR5's on-die ECC matter for gaming overclocking?

Not really. DDR5’s on-die ECC corrects rare bit flips inside the DRAM chip, but those almost never cause crashes during gaming overclocks—stability issues usually come from the memory controller, motherboard, or timings. DDR4 without ECC has been stable for gaming overclocks for a decade. For normal gaming overclocks, DDR5’s ECC is a “nice to have” you’ll never notice; pick DDR5 for the bandwidth, not the error correction.