you'll want to learn the differences between Octalink and Octalink 2 first....they do not play well together...... and both come in a few different lengths too.. as do the "cottered crank" BBs you mention.
Octalink (let's call it octalink1) has ridiculously short splines that are prone to failures...... as are FSA CF cranksets (the pedal inserts are known to get loose in the arms...)

people have been known to "Superglue" the pedal inserts to temporarily cover the symptoms of the loose inserts.
i have an FSA SLK crank here with that very thing done to it... it was on a frame, as part of a 5 bikes/frames buy several years ago, so, luckily, i didn't get burned badly on it.....

and you might find that the big chainring is worn on that FSA........