In this post, Josh from Silca says he worked for Zipp and ran the IO through a wind tunnel:
https://forum.slowtwitch.com/forum/S...ics)_P5988702/
It repeats what's been reported in this forum many times, the IO and 808 are pretty similar aerodynamically - with the 808 being better in some circumstances, but the IO is much stiffer. Plus, there is the mental game - you lose on the same equipment as your competition, they're faster. If you lose on different equipment, it's the equipment.
As for why they don't use 5 spokes in TTs, that probably has more to do with the fact that they use tri-spokes, which are faster than 5-spokes but not as stiff.