Generally used is the "Greenhill" theory of twist, the twist required is the length of bullet divided by 150, times the bullets diameter(in inches).This is most accurate around 1500 fps or less, an it was developed during black powder cartridge days. The length of the barrel has nothing to do with the twist required, except perhaps in pistols. The rule is good is BPCR's of all types, however.

FWIW,
If you read the contemporary literature, the Express rifles were deemed good out to 150-200 yds, but the user had to accept a certain loss of accuracy.  The champions of the express rifles were the Brits, pushing .45 slugs at 1800+ fps with big powder loads to get a good point blank range - but with significant trade-offs.   
I if recall, J.H. Walsh stated that a very good express rifle with perfect barrel (single shot) was considered top-notch if it could put its shots into a 4" circle at 100 - not something that would be acceptable for me...
FWIW, I am of the opinion that overstabilization is most certainly no sin - but understabilization is.

Don, yes the early hunters were wildly succesfull. And we too could be if we had the game they had to shoot at. Just consider what you could do to a herd of thousands of Buffalo with a 300 magnum from 400 yds on a herd that would not even get excited when they were shot at. In Africa the large big game was used to being the top of the chain and instead of running would either stand their ground while they were chopped down or come in closer to be killed easier. The English big caliber Express rifles were succesful because they knew to include big heavy bullets with the big heavy charges of Black Powder and also knew something about  Twist rate. The Sharps Company had a line of Express calibers also but in their case they too used correct twist and just made the shell longer to accomodate bigger charges of Powder. Winchester for some reason forgot or ignored this wisdom of the time and came out with their own line that was a disaster. I had a 38-90 Express rifle and a freind with more experience than I warned me that they did not stabilise very well. First three shots at 50 yds all went thru the paper flat sideways. End of story. made a 32-40 out of it. still have it today 37 years later. Have no idea what I did with that pristene full octagon barrel but it is not in my stable. Well enough of my raving. Regards, FITZ.