Based on your other posts, I'm going to go ahead and assume you aren't sleeping with this girl at least pre-engagement. If I'm wrong, a lot of my advice is probably not relevant.
Ignore most (not all)of the advice from people telling you to live in with her before getting married (including most other things they're saying); they have a fundamentally different world view than you do, and their advice is all geared to that world view.
There is a reason that arranged marriages have a higher success rate, even in the US, than normal marriages; commitment and a willingness to accommodate / love the other person no matter what matter more than the way you feel about the other person going into the marriage.
As far as when is too soon really too soon:
You've dated long distance. That will speed up a relationship quite a bit; instead of meeting up to do something a couple times a week where you might do things which really don't teach you much about the other person, you might talk, face to face, for hours a day, getting to know each other much, much faster than you otherwise would. If you haven't already, you need to actually discuss (in detail) the big issues that can split a marriage up: differences on opinions on religion and philosophy, values, money and careers, sex, future locations, future children and their existence / number/ raising.
If you've done all that, my advice would be to not get engaged / married until you've had at least a couple arguments that have left you steaming even after you've stopped talking for the evening. Also, it would probably help if you did something very stressful where you stay with her and control and personal habits are an issue (like a road trip) before getting engaged. Finally, don't get engaged before you can identify at least a couple of flaws. Make sure you're seeing clearly.
After you've done the above, I don't see there being a too soon; whether it's six weeks or 6 years. (Although if it takes more than 3 years and you both started dating later than high school and aren't in the military, you're probably doing something wrong).
Post Note: I read the thread more completely, and I'm giving advice remarkably similar to Guppy, who has a very different world view than I do. Maybe my advice is more general than I thought.