I do think that Paul is talking about a hypothetical believer. I also think that he can see himself as that believer, and would acknowledge having such painful thoughts either in the past or even in the present.
At the same time, I don't think that he's doing a strict "autobiographical self-expression," the way these words are sometimes construed. There's a sense in which Paul--as a mature saint and minister of the gospel, as one who knows not only the source of this described-soul's frustration but also the correct remedy and response--has gone further, and dwells more and more in the "ch8-experience" than in the "ch7-experience." And I think that the variety of interpretations, even within the Reformed world, reflects the fact that some interpreters recognize the difficulty of trying to peg the Rom.7 man as belonging to one salvation-category or another.
As I see it, the main problem faced by the believer in Rom.7 is that he struggles with the fact of indwelling sin. The young/new believer is the most likely person to encounter the presence of this monster and have it give him that awful PAUSE. "Oh, man! I thought I was saved, a Christian, and everything. And now I've gone and done this! What is wrong with me?" Many people get saved, come to a knowledge of the truth, and they think, "OK, terrific; I'm a child of God... NOW, I can finally obey the law. I can finally be the holy man I've always intended to be, but couldn't because of my sin problem."
And what happens? They wake up, and find out that while their heart now belongs to God (so they thought), hey-o! they still can't obey the law. They still can't please God by law-keeping. And that's what they may well have thought they would/should be able to do once they started on the narrow way, once they started following Christ. C'mon, how many people do you know who've been exactly there. Very, very ordinary stance; and exactly the kind of common issue that Paul, in preaching the gospel and dealing with a series of problems and questions about the gospel, would have dealt with often in ministry.
Yes, Paul can even put himself right there, even writing as a mature believer, right in the questions of a brand new and discouraged believer. "Hey, I deal with sin too; yes me, even after all the years, and all I've been through for the cause of Christ. How do you think I feel about my own indwelling sin? Yep, still got it; still there. Aaaargh! But let me tell you: there is more to the Christian life than this feeling of discouragement. Because there's more to living in Christ than checking yourself against the law 24/7. There's life in the Spirit. Look up to the victory; look not to yourself, but to Christ."
Paul needs ch.7 to properly relate the Christian to the facts of sin and law, in the aftermath of salvation by pure grace; and in advance of talking about Spiritual life.
heehee... consider it post conversion.
