You're never going to find the 'perfect' build, simply because different people have different ideas as to what 'perfect' is. My 'perfect' build would probably be considered a bit overpowered - I'd prefer a quick, clean kill, where the challenge lies in positioning yourself and aiming perfectly. It sounds like you think the challenge should be in the damage you do, and your sneak skill. That, to me, is an imperfect build, but to you is 'perfect'.
So I'd say a very nearly maxed sneak skill - all of the 'sneak is % more effective' perks ought to be taken. You'd have a high archery skill, and a good quality bow - not Daedric or anything, but close. You'd find your challenge in finding a good spot at a long distance from your target. You have one shot - shoot once, watch your target fall and get the heck out of there!