RE: S&W model 36
Recommend that you do not use +P loads for everyday practice in this weapon. Same advice goes for the very similar Taurus 85. A couple of boxes of +P would probably loosen things up a bit too much. A few rounds to see where they group would be all I would risk, then save the rest of the box of +P for carry purposes (if carrying is legal where you live.)
You gotGREAT deal, by the way. These are very good little carry weapons for short range self defense work. You might want better grips though - - the recoil is pretty stout even with mild loads in these little things and better grips aid in controllability.