Last time I talked with someone about this, they convinced me there was some rare, possibly even research-only x86_64 chip that didn't support it, so my point i

Last time I talked with someone about this, they convinced me there was some rare, possibly even research-only x86_64 chip that didn't support it, so my point is that if my hazy memory of someone else's argument is correct, that it doesn't matter, treat it as if it's exactly 100% anyway. It's 100% of what matters, so in practice I'm in full agreement with you.