There is a trade-off; with rifle bullets of similar weight (such as the previously-mentioned .45-70-405), the rifle bullet will have greater sectional density, whereas the slug will have greater frontal impact area. Whether this is preferable
for you will be based on your theory of what makes the best hunting/stopping bullet. Some believe in the TKO, which includes the surface area of the impacting bullet. Others only look at raw energy, which will give a definite foot-lb advantage to rifle rounds.
Think it through, listen to folk you respect, and get really good with whatever you decide to use.
Do you want to hear that dream?