Apartame clarifications

There's a lot of information out there on aspartame (and other artificial sweeteners). I'm looking for some clarification on how it's broken down by the body and what kind of negativity and positivity it offers the body. I'm currently in the process of cutting out sugary products; soda, cupcakes, candy, etc. I understand the healthy types of sugar out there in things like fruit, which obviously I'm not cutting out. I understand the benefits of sugar and what it provides, and how your body needs it for multiple things.

With that being said, for a very long time I was addicted to soda. If you saw me drinking something, it was a soda. A year ago, I quit them, for almost 8 months. Little by little, I've started drinking them again. Up to last week, I was drinking around 1-2 cans per day. I realize this isn't the end of the world when it comes to the human body, but I'm in the process of maintaining a healthy eating lifestyle, and consistant weight-lifting and am getting lots of cardio. I want to maximize the efforts I'm going through (probably 7 hours of cardio/weight lifting per week, with a 80%+ fruit/vegetables diet), so I want to minimize my "bad" foods. One of the things I'm doing is currently struggling with my sweet tooth. Aspartame, according to all reputable studies that I've seen, is not going to be negative towards my body. However, I REALLY want some clarification on how it's broken down. Is it "the same" as sugar? Is it worse? There are plenty of diet drinks out there with aspartame, and I'd really like to know if some of them are "safe to drink". My favorite soda, Mountain Dew Voltage just came out with a Diet version. It tastes pretty similar, but with 0 cards, 0 "sugar" (has aspartame), 0 calories and low sodium and is made with aspartame. For someone who's going through all these healthy changes; how much IS aspartame going to effect me? Also, even if aspartame is "safe", are there other ingrediants within diet sodas that are (very) unhealthy?

A few notes:
I realize everything is okay in moderation, I'm looking for specific clear, factual, scientific information on this subject.
I'm 6 foot 200 pounds, running between 3-10 miles every other day along with lifting weights.
My diet is 80% fruits and vegetables, with snacks primarily being baked chips, light popcorn, etc.