I checked some other sites like 6mm BR.com and most of the long range shooters are going with a 1-8 to 1-8.5 twist for their 6.5/284s. I don't know if the 200 extra fps of the .264 will compensate for a slower twist or not.
My experience is with factory barrels and hunting bullets only. If you want to shoot the 140 VLD's or anything heavier like the 160 Woodliegh I would go with the faster twist. The 142 SMK are said to be marginal with a 1-9 in the slower 6.5s.
As others said try a different scope and load tuning first and you might be surprised with the barrel you have.
Oh, and welcome, we need more gun loonies from Down Under. Typically they have lots of practical experience and a slightly different take on things that's refreshing.
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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