Kewl.

My bet is that it'll take the 65th event, or several 'big-fish' enemy agent captures to get him his 7th star.

Based on geometric progression, six stars means 32 successful events.
I guess that enemy agents are worth so many points, according to their star rating, such that a caught 3-star enemy is worth 4 'points' even though it's only one event. I could be wrong though.

It's risky to second-guess how CA implemented it but you could also apply the geometric progression to an agent's capture probability, with each extra star halving the likelihood.

Say, for the sake of argument, that it's 95% chance of capture at level zero, versus BF's. Halving 0.95 six times in a row (ie {0.5^6}) takes it down to 0.0148 (1.48%), or about one year in 67.

Not utterly uncatchable but very comfortable odds.