I am not an expert by any means, just a varmint shooter with a lot of curiosity. I guess my desire here is for a method to arrive more quickly at optimum accuracy for a given bullet. 
Your SX experience bears out my point. The fast twist gave them more RPM than they could handle even though they were under the suggested speed limit.,ask me why I had to put mine in the Soda cooler to avoid whiteline probs.)
Got some 30 cal info, credit to Mr. Bobbit again:
Here's the minimum and maximum spin rates in RPM I've found works best
with Sierra's 30 caliber match bullets:
     .308 dia.      Min.       Max.
      Bullet        RPM        RPM
     ---------    -------    -------
     150 HPMK     140,000    160,000
     155 Palma    145,000    170,000
     168 HPMK     150,000    175,000
     180 HPMK     155,000    185,000
     190 HPMK     160,000    190,000
     200 HPMK     170,000    210,000
     220 HPMK     195,000    230,000
     240 HPMK     210,000    250,000
 
would love this infor for Ballistic tips, Vmax, Blitzkings, etc.
Think I'll query Hornady.
HM