I'm shooting 139 gr Lapua Scenars and 140 gr Berger VLD's from my 6.5x284. It has a 1:8 twist McGowen barrel on it, and I haven't had any issues with bullets stabilizing.

I started off shooting 142 gr Sierra matchkings, but kept getting single flyers in each group. From talking to a guy at Bruno's Shooters Supply ( I used to live near there), he suggested I switch to the Scenars. My lone flyer issue went away.

Moral of the story, I don't know what bullet you want to shoot, but you may not need that 1:7.5 twist.