A discussion on achievement list design- standard objectives vs. secondary options

Let's say you were designing the Xbox achievements for a story-driven game worth a total of 1000 gamerscore. How much of that 1000G would you distribute toward standard milestones in the game (e.g. beating a storyline boss, reaching a certain point in the
story, beating the game on standard difficulty, etc.), and how much would you put toward optional secondary goals (e.g. side quest completions, optional challenges, collect-a-thons, beating the game on a harder difficulty mode, etc.)? As a bonus question,
how much would you designate for beating the game on standard difficulty?

For most game genres, I'd aim for 300G for standard milestones vs. 700G for optional secondary goals. I think it's important to have a nice balance, and I'd want all players to feel some sense of accomplishment for playing the game even if they're not going
to complete all of its content, let alone finish it (hopefully having some achievements along the way would serve as slight encouragement to keep playing). However, I'd want the majority of the gamerscore to come from optional objectives so as to give players
who want to fully explore and/or replay the game a lot of incentive to do so. I'd make at least 200G worth of these optional objectives easy to accomplish, though, to try to make the player slightly more encouraged to consider trying other objectives.

I think I'd probably designate 50G for beating the game on standard difficulty, maybe 100G if the game is fairly short in length. I'd want this to be one of the highest-scoring achievements in the game.

How about you? What would you choose and why?

:)