I think macro the oGCD with GCD will not really drop dps, like..

/ac swiftcast
/ac shadowflare

This one will use swift cast with shadow flare ready to target in 1 press

or
/ac "Misery's End" <t>
/ac "Bloodletter" <t>
/ac "Heavy Shot" <t>

This will prioritize Misery's end before blood letter and heavy shot, so, when you spam this macro you will use Misery's end when it's available, then blood letter when it's available and heavy shot as filler in-between and it works even better with Wanderer Minuet on