Although there are no rating system in the first game, there is a similar feature in the game, where, if you complete some missions quietly or at least semi quietly, the Desert Eagle will be purchasable on the next mission.
Lee Hong, the quietest way to kill him is to get a bodyguard uniform, meet Mei-Ling, get her out, go in the basement, rescue the spy, get a dragon's uniform, cross your fingers the statue is either near the kitchen storage room or in the brothel, as those are the easiest to rob.
Once you get the statue, you make your way toward Lee Hong's mansion from the front door, and you climb upstairs. Tzun always guard the stairs and the elevator entrance and patrols in a circular pattern, the trick is to study his pattern carefully and walk behind him, as long you stay behind his back, he won't see you and you'll be safe. You go upstairs. Lee Hong can recognize you too, so you need to do the same thing, study his walking pattern, and when he's on the balcony, you make a run to his office and you wait for him with a silenced pistol, once he gets in his office, you shoot him in the head. Some dragons on the second floor might hear him die or see his corpse on the ground and come investigate so be ready to shoot anywhere between one and three dragons, once again, aim for the head, otherwise they'll attack you and bust your cover. That's the trickiest part of the plan.
Once Lee Hong is dead, if your cover hasn't been busted, you walk down the stairs, being careful not to get spotted by Tzun, and when his back is turned, make a run to the front door and the restaurant to give the jade statue to the old man. Then you need to head back to the mansion, and study Tzun's walking pattern, but this time you'll make a run toward the dock instead of the second floor. This part can be tricky too because by now you've been playing flawlessly for fifteen minutes an you'll be pretty nervous about not getting spotted by Tzun and getting to the dock area requires you to press a couple of buttons to operate the elevator.
Surprisingly enough, it is also possible to execute an equally quiet kill of Pablo in the infamous third mission in Colombia.