The CG's were identical. They were within 0.5% MAC.
For the speed calibrations we used a boom. Therefore the should be pretty accurate.
The thought with the trim might good idea to further investigate. It might be that the trim tab was not in the same position. Do you think that this can make such a big difference in stall speed?
Another thing which I came to my mind was that the stall speed were measured at different altitudes. Does anybody have any experience whether this can make a difference?