I just ammo-tested the 455 I shoot the most. I have been using whatever SK Std+ I can get, sometimes a few boxes at a time, but usually a few bricks. I compared 12 different rounds about a week ago, shooting 5 5 round groups with each at 50 yards, paying more attention to the last 3 groups of each since the lube changed for some of them, and ranked them by eye, no measuring (in groups, since I can't rank them 1-12):
Lapua Midas+, Eley Edge, Eley Club, Aguila Super Extra (SV)
CCI SV, CCI Green Tag, SK Rifle Match, SK Std+, Fed Gold Medal Target, Norma Tac-22, Eley Target
Rem 22 Target
These were all the subsonic rounds I happen to have around (other than Rem Subsonic, CCI Quiet, and the primer only Aguila Colibri). I have at least another dozen HV types but I didn't try those.
I will do this again after I pillar bed it, probably with more groups and a little more care. I will also get some more of the Club and Super Extra (SV, and note there is also Super Extra HV, one is red and one is blue on the box).
I didn't change scope at all, and the biggest surprise for me was that the group centers varied so much by ammo type, from dead on with the SK Std+ to an inch and a half high (Fed GM Tgt) to a quarter inch low (both CCI).