If I were going subsonic hunting, I would definitely go with a big bore for anything other than small game (as hinted at by my 44 Rem Mag remark). Personally, I would go with the .338 Fed or 458 Socom from your list. Start by looking at compatible suppressors though. It would be no good to go 458 and not be able to get a can rated for it within whatever budget you have set. You could also look at the 338 Whisper. The smaller case may make it easier to go subsonic.