I've owned E36 M3 with 6MT and 10 lbs of supercharged boost, current owner of a clean AW on cinnamon E46 M3 with 6MT and ethanol (measured 335whp), an F30 328d M sport (wife's car) and now a fully optioned M340i.
Here are a couple of things I can say without hesitation:
- M340 is fast. Properly fast. It will eat my E46 M3 on ethanol for breakfast every time. There is just so much more torque in the stock M340 and the transmission is very quick.
- M340 is a better built car. That is to say that it's structurally more rigid as compared to my E46 M3 and the F30.
- M340 is a very comfortable car to drive (it is my daily driver). All the tech, semi autonomous driving, traffic assist plus, excellent sound system, nice heads up display and all that makes your life so much more enjoyable (I commute 80 miles per day).
- modern generation cars are just better overall cars as compared to even the pure bread M vehicles 5-10 years ago.
That being said, here is where M3 is still an M3:
- the raw driving experience. Hearing my S54 rev to 8200 rpm with the induction noise amplified by a carbon intake is second to none.
- the direct connection to the road. Even when this connection is painfully stiff and you feel every bump.
- the IMMEDIATE, and I mean immediate, throttle response of the gas pedal (as compared to somewhat slower reaction time of the turbo engines).
- the nostalgia of rowing through the gears
- the looks you get on the freeway when you drive your "old" M3.
- the analog nature of it where you have to pay attention while driving it.
I love both cars. I debated heavily between getting a 1 year old M4 comp pack vs a new M340. I test drove four M4s. Comparing the F generation to G generation I can say that the two platforms are worlds apart in technology. F generation plastic feels too cheap, creaky when you push on it and the "stuck on" screen on my wife's F30 feels too dated now.
I thought I'd never say this in my life but I am truly glad that I chose an M340i for my daily car over an M4. M3s and M4s aren't really meant to be daily driven. They're too unforgiving, stiff, and too direct for daily commute IMO. S55 is a brilliant engine but the design language and the atmosphere of F80 is now too dated and I mean it not in a good way
Hope this helps