How do I decide whether to get married?

• My girlfriend of four years and I are both graduating college.
• I haven't found employment yet, and she's returning home for work.
• As near as I can tell, we're very compatible.

Pros

• We are very fond of each other, get a lot of value out of each other's time.
• We've been able to talk about the subject sanely.
• Status
• We agree on religion and politics.
• Married guys make more on average, but the arrow of causality could point in either direction or come from something else.
• Financial benefits

Cons

• Negative Status associated with marrying young?
• No jobs yet, no clear home or area to live in.
• She sometimes gets mad at me for things I'm "just supposed to know" to do, not do, say, or not say. I'm not sure if she's right and I'm a jerk.

She has said that she doesn't want to marry me if she's just my female best friend that I sleep with. But I don't know how to evaluate what she's asking. There are a number of possibilities. Maybe I don't feel the requisite feelings and thus she wouldn't want to be married. Maybe I do have the feelings and I have no way to evaluate whether I do or not. Maybe I'm not ever going to feel some extra undetected thing X, ever, and so I should just go through the motions saying that I do, and our marriage prospects are entirely unchanged. Maybe this is just some signalling ritual we have to go through.

We both are concerned that I've not really had a relationship not with her, so there are no points of comparison for me to make.