Transmission rate is the only metric with any meaning in this context, because the transmission rate is the product they’re selling to you. The overprovisioning and etc is actually accounted for in the transmission rate they’re selling you.

What are you talking about? Overprovisioning literally means selling more transmission rate than what the upstream lines can accommodate. It is not accounted for. Therefore, you only get your advertised transmission rate if your neighbors are not fully utilizing theirs.

Accurate enough for who? It wouldn’t be accurate enough for me.

How can it not be accurate enough when it is just a conversion from transmission rate via a formula that converts to bytes and accounts for expected protocol overheads? It’s the same number, converted to easily understandable units. If it is not accurate enough, neither is transmission rate.