You can put any c2d in there. i5 and i7 are different slots so wont fit.
I would suggest a P series as they runcooler.
Also its a PITA to install a cpu on the studio as you have to take the whole laptop apart to get to it.
If you need a hand give me a shout, have done a few studios. Also have a P9500 for sale, if you are interested I can list it in the members market