Be careful here as CDV upgrade on non M cars is definitely worth doing. However, on M3 at least the CDV is full bore. Assuming 1M is the same then CDV swap out would yield little or no benefit.
I upgrade to an M3 CDV on my e91 335i and difference in clutch feel was night and day.
However, clutch pedal stop mod is worth doing to reduce the clutch travel.
I fitted the BMS one and it's good as its got packers so as you can adjust to best suit yourself and make sure there's no dragging of the clutch.
Just my 2 cents worth.