16 rax - 2x reaper
20 factory - hellion then widowmine
28 techlab on starport
34 banshee & cloak start @ 3:09
34 reactor on rax
banshee arrives at enemy base and cloak finishes @ 4:26
third cc, double marines, tank, raven
standard marine tank-vac viking play as taking third
Keep in mind this was taken from a VOD and not a replay. I tried the build myself and my first banshee finished at 3:50 with arrival cross map and cloak finishing at 4:28
This is not the fastest possible banshee build, you're getting two reapers, hellions and mines to harass with while the banshees finish, I think you need to do *some* damage with the reapers and maintain solid map control with the hellion.
This makes for a very late natural expansion but you're taking a third almost immediately after. Hard to say what the breakeven damage is but it is clearly substantial.