This is what I suspect is going on. The guy in Romans 7 is a pre-New Covenant Pentecost era brother. He's regenerate and loves the law but he is powerless to walk in it as he would desire, at least not until the event that defines Romans 8 comes along. 

With Romans 8 there's a newness brought to that same man through the Spirit Indwelling Inscription accompanied by all of the dynamics resulting from such a new relationship. He experiences a shift that is brought to pass through the ushering in of the New Covenant era by the indwelling Spirit of Christ or better yet, the Triune God.  It's the very relationship the prophets and Jesus had predicted (John's Gospel - The Book of Glory). 

So then,,,, Chapters 7 and 8 are not about who was that man. It's all about an event that has radically changed the dynamics of holy living for that man. It's the IN CHRIST relationship we as New Covenant believers are to walk in.

There is therefore NOW no condemnation to those who are IN Christ Jesus, who do NOT walk according to the flesh, but according to the Spirit. For the law of the Spirit of life has made me free from the law of sin and death. (Rom 8:1-2)  

C'mon guys this is New Covenant stuff and it transforms!

   Moe