I don't usually buy straight calls below 40delta, even if CML shows better results. Although it seems obvious that if a trade is working due to gamma gains, the lower delta strikes will make more on a percentage basis, that works both ways - it will lose more on a percentage basis when it doesn't go your way. Since these are already pretty high risk/high reward trades, I don't see the need to add more risk/reward by going with the lower delta trade. Doesn't mean my way is right, but that's the way I view things.