~*quickload*~ tells me that you might get 30-50 fps more from a long action 6.5-284 loaded to 3.2" as opposed to a short action 6.5-284 loaded to 2.9"
If it's a custom barrel, loading mag length to fit the throat etc is irrelevant as you have the throat cut for your short action mag length loads.
If it's a Blaser it's irrelevant because you own the pinnacle of bolt action rifle design.
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