This sort of gain is totally possible.
Upgrading the CAT's and exhaust alone have proven to give some very good gains as per Supersprint's testing.
That's 20hp alone and the one thing we can confirm is that independant testing of Supersprints exhausts on our dyno's shows pretty much the same gains time and time again.
The GruppeM intake has been tested outside of gruppeM and that certainly increases acceleration. Increase in acceleration will equate to a noticeable gain in hp.
Coupled with even a tame ECU remap your going to get a realistic 40rwhp gain.
It's good to see the M3 has some headroom.