You can use this link to tune your velocity and bullet for the twist rate of you gun. I agree with everybody so far. The only thing I would have a different opinion on would be going to a faster twist rate in a 22-250 for varmint hunting only. You would need to shoot heaver bullets and they are usually not as frangible as the lighter bullets and that does create a ricochet risk. My state allows deer hunting with 22cal center fire so if want the rifle to be dual purpose then use the formula link to figure the twist right for your purposes. I shoot the 55 gr Nightmare Varmint Extremes from Mid South Shooters Supply and they shoot under 1/2 at 200yds from my 1/14 Rem 700 and do exactly what they are called on Coyotes. Here is your link.
http://kwk.us/twist.html 
