I didn't chrono mine yesterday, but I did the night before - a pretty consistent 805-810 with Express.
On the zero range my pellets were coming in bang on for my 45,50,55 yard marks and oddly enough I wasn't getting much wind either - a couple of pellet widths at 55
I wonder if that was it - I'd imagine if speeds went up to 860's with Express that may well have destabilised the pellets at that speed. I didn't feel I shot particularly badly, I just didn't hit that many killzones. Not sure whether to try to draw any conclusions from yesterday other than I fricking hate springers