A 284win will work in a short action, but the projectile gets seated so deep in the case may as well go for a 7mm08.
Really anything mentioned so far would work at the ranges you are talking.
Pretty apparent that brass/dies cost and selection isn't a factor so pretty much anything goes.
Go for 6.5saum, sound like the most bestest 6.5 cartridge at the mo, and it's more exotic than a plain ol' 7saum.
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