That would be an easy one for me Pluckit. Round balls and .54 caliber are a perfect match. So it would be the 1:70 for me.

The 1:28 twist GM barrel is wonderful in .50 caliber - lots of sabot and bullet combinations. But I just can't get excited about a fast twist .54. If your shots are normally 100 yards or less a 223 grain .530 round ball shoots pretty flat and will do a good job. If you want horsepower and range I think the .50 is a better choice.