I think I would lean towards the 175s as well, for that really longer distance.
Get a better stock. Mcmillan, Manners or maybe an HS Precision. Bed it properly.
Then, your groups will tighten, depending on your barrel quality.
To get the group to tighten to the optimum, you will need to work up in small increments, testing each loading fairly extensively, to get which load gives you the vibration around that "sweet spot". Just picking a load and randomly shooting it to see if it works is like trying to pull a lotto ticket for a win, at random.
Systematically working up a load, after first removing as many eratic variables as possible will give you the results which will shine for that rifle. It takes, time, trigger time, and a fair investment in components.
Additionally, the trigger adjustment and trigger quality can have a pretty big factor, as well as quality of optics at the ranges you are talking about.
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