My brother just got a 2016 BMW 340i. This has the B58 engine, same one as the Supra and Z4 (albeit slightly detuned). He was showing me an ECU flash he's gonna get - it's a tool that plugs into the OBDII port, and connects to your phone. He will have 4 different maps: Stage 1 maps (91, or 93 octane) and Stage 2 maps (again, 91 or 93 octane variants of each). And he's able to flash any of them at any time, he also has datalogging capability via bluetooth. The dyno charts look sweet - stock his car puts down about 315WHP. On the Stage 2, 91 octane map, he'll get ~425WHP, and ~505WTQ. ALL STOCK OTHERWISE. WTF! Haha.
I know ours are similar with the JB4 on Map 3+, but you need more than 91 octane to do so... His car will be faster than mine after he starts doing his exhaust. And he only paid 20k. When mine is all said and done, I may be at 450-470WHP. But he'll be right behind me with just a tune. After he does full bolt-ons, I'm sure he'll be making even more power than me. :c
Don't get me wrong, I love my car, and the luxury inside is top notch (much better than his 340i!), and I like our AWD system (again, better than what he's got!). But I'm not the happiest owner because of my partial warranty, nor am I happy about the tiny turbos and the difficulty of doing potent mods (ie bigger turbos, downpipes). And to top it all off, my local dealer are a bunch of scumbags, and Genesis USA is ready to remove your warranty at a drop of a hat, or in my case a snap of a stud (lol). Perhaps my next car will be a used 2020+ M340i or something. Hopefully Mazda finally comes out with an RX8 successor - though, I'm not holding my breath for that. Lol. Whatever.