Wrong. We want to know how quicka car can go with the same driver. That's the only valid comparison we have when we want to know how fast a car can go compare to another.
I prefer an unbiased laptime over a factory time. Factory times are only about markeeting.
The problem of factory times is that they can be wrong for marketing purpose, but factory drivers can make the fastest times, what mean reach the full potential of the car. You want one driver but that is unfair, because take for example HVS, he'll always be faster in a Porsche than in a Ferrari.
BMW gave the E82M an official time of 8:15 min and that is also the time of Sport Auto. But in fact it is faster. In this case for marketing purpose BMW decided to make it look slower than the E92M. The E92M has an official time of 8:05 min, but it had Michelin Pilot Sport Cup+ tires, whereas the time of the E82M was made with the normal tires of the E92M, Michelin Pilot Sport PS2. The time of the E92M with stock tires is 8:12 min, a 10 second improvement over the time of 8:22 min of the E46M. The time of the E92M on stock tires is from a brochure. The time of the E92M ZCP is below 8:00 min on new Michelin Pilot Super Sport that are now stock tires.
E46M on Michelin Pilot Sport PS1 in 8:22 min
E82M on Michelin Pilot Sport PS2 in 8:15 min
E92M on Michelin Pilot Sport PS2 in 8:12 min
E92M on Michelin Pilot Sport Cup + in 8:05 min
E92M ZCP on Michelin Pilot Super Sport under 8:00 min (no time officially announced)
All that, to say that numbers we need are factory ones, but proven and controlled by independants.