I shoot a .243 Ackley Imp. with a 9 twist 27" heavy varmint contour and shoot the 105 A-Max's very well. They run about 3250fps With N-165.
Took my antelope at 375 this but wanted to try an 800 but they were bunched just too close for the wind I had that day. They had been hunted for over 3 week on that ranch.
The 95 Bergers shot alot better than the 95 Bal-Tips for me but had to run them no faster than 3250, duh, try the heavier bullets.
I think the 107SMK's call for the 8 or even faster twist
The 6-06 has always impressed me and if I ever shoot the barrel out on that 270 it will become a 6-06. The 24" barrel will lose some velocity @ 30 fps per in and may give some muzzle flash if your powder is too slow.
The cost will depend on the individual 'smith you employee to do your work. Get an idea from the links below.
Welcome to LRH! Alot of great folks here.
Welcome to Shilen Rifles, Inc.
PAC-NOR Barreling, Inc. - Price List