General Slant and Gas/Octane ???

Okay so my slant 6 runs pretty good regardless of what octane gas I put in but I have found higher octane gas changes the driving range. What I have found is low octane gives me good take off mid grade gives me good mid range power the 50-70 range and I have not tried premium yet. Is this normal or do I possibly have something off? Also I idle better with mid grade.