The way I try to maximize speed downhill - and I run a compact 50-34, too - for me is to go briefly well in the red on the flatter bits - spin out if need be - then tuck in as best I can to recover. Over some speed it's just not worth pedalling because the aero losses eat it up, unless you're really laying on the power, so go in the red, tuck in, recover, and go again seems to be overall faster.
It's fun when the visibility is good and you get a workout downhill.