It seems I am suffering from something similar. 07 335i with 52k miles on the clock.
No miss-fires as such, just a jerky sort of on/off wobble in 4th, 5th and 6th at 3-4k rpm. It does seem pretty specific to that rev range and no issues elsewhere.
Will book it in for check up at an indy soon, but have a suspicion carbon cleaning maybe needed.