I tested in the open field at Blaenau Gwent on a blowy day, same poa at 55yrds I then alternated between 8.4 & 7.9 nothing in it really. I did notice the 7.9s were more consistent on the horizontal. The 8.4s would go above and below but the 7.9s seemed to stay on the line.
Then group wise mine liked the 7.9s
That's as scientific as I got :-).
Steyr LG110 FT, Sightron SIIISS 10-50x60 LRIRMH