Hi'all thanks for all the responses on and off line. I have a more clear picture now.
An IM 7 might cast for longer distances, if I ever will be able to do so. Because the material is more stable, the rods/blanks seem to be build with thinner walls. This leads to an increased chance of damage due to mishaps (collisions with heavy flies,..) and a breakage later after the mishap.
The rods I build in the past were build on IM6 blanks. Therefore I have an idea how IM6 casts - if we ignore the taper, this is probably wrong.
If I read all your posts, I see how much time y'all spend to answer me - this is really a great group;
Thanks a million Rene
