My memory is that the 335 and M3 are about a wash in terms of highway stability, and that's because the M3 has some advantages and some disadvantages. In the advantage category, it's got larger diameter and fatter tires, and a larger contact patch generally means more stability (unless your tires are so large and grippy they start following pavement grooves, which the M3 doesn't). The M3 is also heavier, which makes it feel more stable. On the other hand, it's got a much quicker steering ratio. The steering feel is also heavier (even in Normal mode), but that doesn't come into play when dealing with external forces rather than your steering input. So if all else were equal, the M3 might be a bit more prone to getting nudged off course with cross breezes from traffic going past you quickly and such -- but all else isn't equal, so it's about the same, and of course it's not as if much traffic would be passing you quickly.
Passing? As others have said you'll definitely need to shift to 3rd to get that rush you're talking about. Accelerating from 65 in 4th definitely doesn't feel weak (still faster than the average car will manage in their lowest available gear for that speed), but it's slower than you'd expect for an M3. But that's what those extra several thousand revs are for!
Bottom line: If you want to drive lazily in terms of shifting on the street and freeway, the M3 will feel "adequate" to "good" in the acceleration department. But when you want to go out and have a good time and are therefore prepared to downshift, it's a whole other game.
