only the most veteran of BG players ever realize that the Rogue is in fact the most broken, OP and fun class to play...
between the stealth skill, backstab x5 (x7 for assassins), invisibility potions and haste potions/boots of speed, FEW mages could survive more than a few seconds against a well prepared rogue...even Irenicus was turned to mush by well placed traps before he could even get his contingencies off. Dealing with fighters was just a matter of speed/poison/backstab/arrows and everything else was just fodder.
so as to the question of stealth killing in a game? HELL YES, NO QUESTION ABOUT IT.