Hi. I have 2 Steyr's that are set up to shoot with the same fit and POI with the same pellets. Also the same scope. Nothing between them for accuracy but one is slightly more 'dead' to shoot despite both having exactly the same dimension settings on the stab spring.......air rifles eh?
i also have a Vmached TX200 that is just bedding in and showing some promising signs.
I shot for the Daystate team for HFT a while ago and found that the Daystate CDT and electronic triggers showed some of the best grouping ever on the zero range but i would always be 2 or 3 shots below my normal scores. I wasn't the only one that found this. I'm not sure but my thinking was that it was the slighty snappy shot release that was made worse when resting against the peg in HFT...somewhat akin to springer hold. Still can't explain it to this day but i perservered for a year befpre switching back to the Steyr.
There's a lot to be said for sticking to one gun/scope combination and learning that set up inside out. The variation that comes from shooting HFT courses shows a totally different picture than when you're on the zero range for an hour. I would personally try 7,9gr AA's in the S400 and check for grouping/POI and trajectory flatness.......you might be pleasantly surprised as i'm getting some very good results with them.