A slower twist does not put as much spin on the round ball. With too much spin you get a 'curve ball' like in baseball.
However a conical likes spin sort of like the 'spiral' on a football. 1:48 does a fair job with both, but overall a 1:60 or
slower will shoot a round ball better and 1:30 or faster will shoot a conical better - of course that depends a whole lot
on the size and the hardness of the bullet, the powder charge , the particular gun. No easy formula here and of course
thousands of opinions on the subject.