Bear in mind also that your barrel will have been 'leaded' by the old pellets and it will probably take a 100 or so shots to 're-lead' your barrel with the new pellets that were almost certainly made from a harder or softer alloy of lead.
Dismissing the new pellets after a small number of shots will serve to prove nothing.

I use RWS geco's through my Morini and another shooter (better than I) at the club puts them through his Steyr, we have both fould that rested the gun's are still capable of large single hole groups - so perhaps some of the 'cheapies' are not so bad - your own testing can determine which are better for your gun.