> I feel like potentially reflowing BGAs on a high speed I/O PCBA y
If you're trying to get chips up to something less than 100C, but instead get stuff underneath it with significant thermal mass up to above 200C, you're really messing up.
Hair dryers tend to emit like 65C-70C air on their "high heat" setting (as opposed to hot air guns used for heat-shrink and reflow soldering).
Link training can be disabled in the BIOS, which would make searching for borderline bandwidth settings a quick operation. The results would not be very repeatable, but that's not important.