Was Paul assured of his salvation?

A view that is prevelant in Protestant theology is the idea that justification is a one-time, irreversible event. I've heard this described as the "once saved, always saved" mentality. That is, once someone has been justified (I'll leave any discussion of how someone can be justified for a later date, or better, for those with a real knowledge of theology), the process of justification cannot be reversed. People are justified while they are alive, and no matter what they do after that point of justification, they cannot lose their salvation.

This idea certainly has its merits, although I don't believe that it is held by many in Catholic theological circles.

In his first letter to the Corinthians, Paul makes an interesting statement, that I believe sheds some light on this issue.

But with me, it is a very small thing that I should be judged by you or by any human court. I do not even judge myself. I am not aware of anything against myself, but I am not thereby aquitted. It is the Lord who judges me. Therefore do not pronounce judgement before the time, before the Lord comes, who will bring to light the things now hidden in darkness and will disclose the purposes of the heart. Then every man will receive his commendation from God. (1 Cor. 4:3-5, emphasis mine)

I think Paul is clearly discussing justification, since he uses the legal language of aquittal. Also, what could a "commendation from God" when the Lord comes be other than salvation? Paul acknowledges that although he doesn't know of anything that would prevent him from receiving that commendation, he also doesn't know sure that he will receive the commendation. It is up to the Lord to judge him, Paul won't even judge himself.

It seems like Paul was not certain of his salvation. If he wasn't certain, I don't want to claim that I am.