i used one and there was no difference,,i have to say that in my opinion ngk c7hsa was much better,, i had used it on both stock dhoom 70 and altered dhoom (110cc) no difference as of now,,
and as far as the copper core is concerned it means the inner conductor ( not the tip ) and all standard plugs have copper cores,, as i found after searching for it,,
don't know about the racing plug that is mentioned above,,
currently i have installed the autolite plug and have done approx 1000 kms on it,, will update u if i notice any speciality,,
oh i also tried the side gaping ngk plug on 70 and that was awesome ,, bike sounded much smooth, and was quite responsiveness,,