I was reading George Eldon Ladd's The New Testament and Criticism and noticed that he, like Ehrman in Misquoting Jesus, addresses Romans 5:1 and the issue concerning the reading of either ΕΧΟΜΕΝ (we have) or ΕΧΩΜΕΝ (let us have). The first being an indicative, the second being a subjunctive of exhortation.
Ehrman has this to say about the verse:
And so in a large number of manuscripts, including some of our earliest, Paul doesn't rest assured that he and his followers have peace with God, he urges himself and others to seek peace.
Several times in Misquoting Jesus Ehrman comes close to insinuating that entire theologies are built upon single verses. For example, in regards to 1 Timothy 3:16, Ehrman states that the verse "...had long been used by advocates of orthodox theology to support the view that the New Testament itself calls Jesus God." However, he doesn't mention that the theology of Jesus being God certainly doesn't hang upon whether this verse reads ΟΣ (who) or ΘΣ (the nomina sacra for θεος which is Greek for "God"). Take it away and you have no problem constructing a Jesus who is divine.
So, back to Romans 5:1. We have what seems to be equal weight with both readings. But lets suppose that the original text read ΕΧΩΜΕΝ. Do we have a problem? Does Paul believe that we don't actually have peace with God yet and that we should seek it? I don't think so. For one, Paul's readers would not have read this verse in vacuo. Paul has already mentioned "peace" from the Father and Jesus in 1:7 to those who are called "saints". Later Paul writes in 14:17 that the "kingdom of God is...righteousness and peace and joy...". This also seems to coincide with Paul's thoughts in Galatians 5:22 where he claims the fruits of the spirit include "peace".
Secondly, the idea of the subjunctive meaning that the saints to whom Paul wrote did not already have peace seems wrong to me. "Let us have peace" could equally mean "let us continue to have peace". For example, in 1 John 4:7 John writes, "αγαπητοι αγαπωμεν αλληλους" (Beloved, let us love one another). Do we really suppose that John meant that they had not previously loved one another or is it more likely that he was using the subjunctive to encourage his followers to continue in love for one another?
The idea that the saints already have peace is indicated by the present effects of the "justification" in vs. 1.
Take a look at vss. 8-10:
A. We were sinners, Christ died.
B. We are now justified
C. We will be saved from wrath
A. We were reconciled by the death of Christ
B. We are currently reconciled because of the death
C. We will be saved by His life
According to Paul, we are currently justified and reconciled. So, if 5:1 reads "let us have", I don't see it as Paul doesn't believe he has peace with God, rather Paul is encouraging his followers to continue in the peace of the current effects of salvation.