I disagree, to most enthusiasts Lag is the revs at which the Turbo is capable of producing boost. Technically known as Boost threshold.
Lag technically is the delay between throttle application and power delivery when the engine is in the boost threshold region.
The fact that the new M3 has at least 2 turbo's sequentially set up, and a very short plumbing through an water/air intercooler, to me means that it will be significantly better than a 335i in both boost threshold and Lag terms.
The major plus with a Turbo is you have a massive torque band.
When you undertand the real term of LAG, an NA engine has LAG ALL THE WAY TO REDLINE, at it never has that boosted torque increase.
Unfortunately you always seem to get NA or Turbo enthusiasts. It is usually one or the other as a preference.