Just bought the movie adaptation. Six issues long
But that was spinning out the adaptation (with bonus scenes) to maximise a guaranteed best seller, cashing in on the successes of "Countdown", "Nero" and "Spock Reflections".
which re-enforces my view that 3 issues per story would be the right length.
Not too sure if these figures tally with IDW sales, but I have been doing a course in Creative Writing and the lecturer mentioned the rule-of-thumb financial realities behind the current trend with trilogies to tell a story arc. A best selling trilogy can certainly hold (or increase) its audience, but a regular or mediocre trilogy will probably sell just two-thirds of Volume 1's sales for Volume 2, and two-thirds of Volume 2's sales for Volume 3.
If IDW stays with duologies, chances are the sales will reset every second issue instead of following the law of diminishing returns.