Windy,

As to the .256 Mannlicher (6.5x54) employing neck or high shoulder placement :Never had a "failure" with 160 Hornady or 160 Sierra in Norma case and MRP at 41 to 42 gr (depending on which weapon I loaded for)(REDUCE in your gun and work up).
Whether, Whitetail, Hog or Elk (within suitable range, less than 250yds)all hit as intended crumpled.
If I do my job it always does its job.

(While a 180lb Whitetail hit 4 time in the paunch (scope failure) with a 45-70 left the scene after being bowled over each time at 110 yds)(many years ago and still haunts me)

All of the cartridges you mentioned I have loaded for and used at one time or another and have nothing bad to say about any of them. The "litte" gun is however my favourite after 40+ years of hunting, though I leave it in the scabbard for the long range (250+) and the heavies (bear etc)

My boys have used its relative (near twin) the Swede 6.5x55 very well as they progressed from heart/lung to high shoulder placement. This load is a Barnes X or TSX 130gr (faster and flatter)
is equally devastating.

Keep the "little" gun and enjoy.

DuggaBoy