Very interesting thoughts! I perhaps dont eat steak often enough to notice such a difference.
I believe steak has a higher creatine content than most other meats. This might be an explanation for beginners or for those not supplementing with creatine monohydrate.
However in your case, this little extra creatine would hardly make a difference as through supplementation you are probably already up and the upper limits of total muscle creatine content.
Perhaps its just because it tastes so darn good! that drives up your feeling of wellbeing, driving up your self efficacy, improving your overall performance!!