edge,
Sorry to leave you hangin', I dropped the ball on this thread.
Here are the minimum twists for the bullets you mentioned at the velocities you gave
(3000-3100)
168VLD) 1:12.8"
175VLD) 1:12.7" to 1:12.8"
185VLD) 1:11.8" to 1:11.9"
190VLD) 1:12.1" to 1:12.2"
Keep in mind there's a little wiggle room in these twist rates. If you just go by the recommended twist on the website, you'll be ok. I hesitated to even use one decimal place in the numbers, it suggests a level of detail that's not really necessary. Of course faster twists are ok.
RR,
For the BT bullets, minimum twists are:
168BT) 1:13.1"
175BT) 1:13.4"
I assumed ~2600 fps muzzle velocity.
The BT bullets are more likely to work at mag length (off the lands) than the VLD's. They're what we call 'length tolerant'. However, the BT bullets have thick jackets, and are not designed for expansion. In other words, they're not hunting bullets.
-Bryan