I stuck with the 172.5 crankset. I ride a 54 road bike (52 cannondale cross and 54 empella cross). The longer crankset was a trend around late eighties to early nineties with big miguel indurain using long cranks and winning the tour. There has been a few studies where they test power vs cranklength and no one has proven that longer cranks produce more power. I know that physically the torque is increased with the length of the lever arm but the biomechanics of it seem to be a bit more complicated. Thats why you have some track riders on 165 crankarms. I have the 175 on my mountain bike where the lower cadence is more common but when cadence and endurance are involved, i'm sticking with the same size crank as my road bike. Also, my toe can touch the front wheel with 172.5 cranks when i'm clipped in but i've never hit my foot with my tire while riding.
As for chain drops, it happened at two places on the race course. One was a downhill with a bumpy corners where I was leaning over. The other was a really bumpy flat following a remount. I'm not sure if additional chain tension from a shorter chain would have kept it on. It also may have something to do with the chain line. I had the single ring mounted on the inside chainring location and was in a small rear cog (downhill) when it usually fell off to the outside of the chainring.