Testing the bookends of BMW’s supreme B58 straight-six engine

Z4-based Supra has aged beautifully, but how does it compare to the X3 M50?

If I were to gaze into a crystal ball and predict what kinds of articles classic car magazines will be pumping out in 25 years’ time, staring back at me from within the quartz would be one letter and two numbers: B58.
A few pages on the history, the birth, the need for a new adaptable straight six that could handle a few configurations would be a gimme; a double-page spread on its tunability and value for money on the used market another. But the big cover lead would be a group test of every car this engine featured in, from BMW 3 Series to Z4 with Toyota, Morgan and Ineos thrown in for good measure.
The article you’re reading now, however, is a more personal tale rooted in my love of this engine. To explain it, I’ve pitted an X3 M50 against the B58 car I think it’s most different from: the Toyota GR Supra.
On a superficial level, the hot X3’s brashness only highlights the Supra’s beauty. When I first saw i