I switched from a triple chainring setup to a double and the new cranks were carbon. It made my feet feel so light it was unbelievable, like the spring time switch from hiking boots to sneakers.
I know that single sided Look pedals weigh less than the Quatros, did you also switch to lighter shoes?
If so that would explain it for me.
By the way I second the notion that Look pedals (or in my case SPD-SL) are easier to get into. I clip in (or stay clipped in at stops) with my right foot and run my left foot over the pedal and the nose of the cleat catches, I start pedaling and am instantly clipped in without looking down.
As far as problems unclipping from SPD-SL pedals, if you are using road shoes I can't see why they would cause a problem. Now if one was using MBT shoes with SPD-SL pedals, then I could see how the rubber sole might catch.