Just curious if I missed anything:
18% Natural Fighting
3% Artifact Black Dragon Helm
9% Skirmisher's Bracers OR centered w\ First Blood 13%
6% Hail Of Blows +Running with the Wind GMOF twist
10% Grandmaster Wind Stance
5% PTWF
20% Killer running at full (implies 10\9\1)
51\55 Doublestrike without\with first blood
71% Doublestrike with Killer.
101% if you turn the jets on (But which would be better at that point, haste boost or doublestrike boost?)
Is that pretty much max doublestrike?
Bard song could be six more. Not going to add in shadowdancer profane DS because I'd hope you're not using that destiny on this kind of build. If you went 10 rogue you could also get opportunist. Also, going grandmaster of forms hurts because that split is already short on feats.
On a side note, going 9\9\2 ranger and picking up Killer that way could be fun because archer's focus