Until this point, the M5 was almost always the best car in its class:
E12 M 3.5i: had 218 hp in the late 70s, on par with a base Ferrari. And not to mention it got all its engines from the just as sporty 6 series. Everyone else requiring at least a V8 to get those numbers. Or a turbo.
E28 M5: cranked up those numbers up to 286 hp. Unless we're talking Hammer (and those were easily 3x the price) there was no match to this power sedan.
E34 M5: the playing field got a little bigger with the 500E and the Lotus Omega, however BMW was the only one who didn't require a different company to achieve those numbers. And still reigned supreme with a N/A six cylinder engine. Mercedes needed a 5 liter V8, the Lotus a twin turbo setup. If you're counting Alpina, it was still the fastest (in a straight line).
E39 M5: this was the deal breaker: almost 5 liters of displacement, V8, manual, and 400 horsepower. No one had an answer to this until in 2001 Audi released the RS6. Which again, needed turbos to put down those numbers. The design was so sleek, it could reach 300 kph several times when tested without limiter.
E60 M5: this thing got a racing derived V10 engine. One impressive machine, albeit unreliable. It may not have been the fastest around its time, especially when seeing the potential of the E55 AMG, but it was still more than a solid contender and actually capable on track despite its almost 1.9 tons.
F10 M5: it's hard to defend the F10 honestly. While a twin turbo V8 can be great, it didn't have the same aura as the other cars in its class. Also was surprisingly heavy, especially compared to its newer model. Traction only was there 2 times a day, and even the claimed acceleration figures were more or less inaccurate. It was cool that it could reach up to 600 hp but that wouldn't save it from being outclassed by the RS6 Performance or the E63s. Or hell, even the Cadillac CTS-V
