From what I've heard here's the lowdown:
Outfits provide stat boost and there is no armor value.
S improves combat damage and helps with some stat checks
P improves combat damage and helps with some stat checks
E reduces damage taken and greatly reduces radiation damage (10 is radiation immunity, 11+ actually gets treated as negative radiation damage)
C helps with some stat checks in the waste (e.g. freed slaves recognizing you as friendly)
I helps with some stat checks in the waste (e.g. you successfully bandage the wounded sheriff)
A improves combat damage and helps with some stat checks
L Increases chance of item drops, but not rarity
As far as combat encounters it seems to be a bit more complicated. Failing a stat check based on the encounter could require a higher overall damage output to win the fight. For example an A of 2 is enough to be faster than a Rad Roach in the beginning and automatically win that fight most of the time. However failing to have an A of 2 means you have to have more combat damage or be higher level to succeed in that fight. The win/loss messages tend to hint when you fail a stat check that could have won the fight instantly. (The Rad Roach was too fast for me, I have to run! or Despite it's speed, I managed to squash the Rad Roach)