Ok so 1 in 10 is not the best for bullets 90-100 grains? How much extra is it do you know?You can custom order Coopers with your desired twist(cost extra). I just ordered two a couple months ago. Lefthanded, faster twists, and pic. rails. They were around $2100 each with a laminate stock since composites aren't offered in lefthand. For the 105's in the 6br improved's the 8twist is the ticket.
Hope this helps