I know you said you cleaned and greased the pedal threads, but by chance are they not tightened enough?
The reason I ask is that I had the exact same problem as you (click at around 10:00 on the non drive side, could feel it with my foot, only under load). I tried EVERYTHING I could think of, including installing a new BB. Got on the bike after that...still clicking. I figured due to the nature of it that it had to be at/near the pedal because I could feel it, and it went away if I unclipped my left foot and pedaled only with the right. I took the pedal out and re-greased it (again; I had already tried it), but this time I bore down on it really, really hard and got it way tight. That was last fall, and I've got 2,500 miles this year and still no click. Just thought I'd mention it.