Decided to try the Shimano conversion kit for Vector 2 with the Shimano Ultegra PD8000 pedals. Garmin doesn't officially state whether this should work however i'm pleased to report it works fine. Seems the pedals axle in the 8000 pedal is exactly the same as the 6800, all they changed was the pedal body material making 8000 slightly lighter.
With these pedal bodies, they feel significantly lighter than standard Garmin vector 2 bodies.
Pic here: 
I know this is old tech now but thought i'd let everyone know, think these are the only Shimano power pedals available still. 6800 pedals are very hard to find new where as 8000 is easy.
