For the clearest understanding of KJV lingo I highly recommend the Oxford Universal Dictionary, any edition from 1933-1955 (used booksellers list them for around $20 USD). Mine defines "chief" as:
Chief, adj + quasi-adv: 1. head 2. at the head in importance; principal, foremost [most notable or prominent], greatest.
With Paul's awful record of wasting and wreaking havoc in the early churches of God (most notably his role in the stoning of Stephen), and beating and imprisoning believers in every synagogue (Acts 22:19-20), it seems that "Chief (foremost, most notable or prominent) Sinner" would be an apt title for him, without exaggeration.
You mentioned conflicting Bible translations. I believe there sometimes may be minor insights gained by comparing and contrasting various renditions of a difficult passage of scripture. But we might ought to weigh the value of those insights against the potential damage caused by a process that naturally erodes our confidence in the divine inspiration of the message we are trying to understand. How many different ways can we interpret the meaning of something divinely inspired, before its divinity begins to suffer?
Carried to its natural conclusions, our 20th century tradition of perusing many different Bibles while exclusively trusting no Bible in particular provides for us a doctrinal foundation of ever-sifting sands, and a reality where essentially nothing in the word of God speaks with absolute authority and every word of God is fair game for revision ad infinitum. Finally, the academic pastime of coaxing nuances from Paleo-Hebrew and Koine becomes more important to students of the Bible than putting line upon line and comparing spiritual things with spiritual, that is to say, rightly dividing the word of truth.
So I think settling on one particular version of scripture as your trustworthy "oracles of God" may better serve you in the long run than the practice of consulting multiple Bibles, which in my experience only ministers questions rather than godly edifying.