Options.
NEITHER
I push a 139gr 6.5 Scenar at 2900fps out of my 6.5 mystic (my version of the 260AI). This I feel gives the best of all worlds balancing wind drift, recoil, barrel heat/wear, costs. The 6.5 Swede gives near identical performance but I like using 308 Win brass and sharp shoulders.
I feel the 6.5-284 case is not as effecient as I would like. I am duplicating the performance and using less powder. Most VLD 6.5s shoot best from 2800 to 3000fps so a larger case serves me no purpose.
The 6BR and derivatives are a great bunch of cartridges. Wonderfully accurate but will get bounced around more then the above. It also cuts a smaller hole which will eventually mean a missed point.
The 7mm (180gr Berger) offers better wind drift when pushed to 2900fps or faster. But that comes at a much higher recoil, barrel heat, costs, etc.
As they say, there is no free lunch.
Decide how far you will be competing and how much driving you want to do.
Jerry