Well you should know that there are several more factors beyond twist, caliber, and round ball vs. conical. The depth of the rifling, the style, and how smooth the barrel interior after the rifling was cut are also big factors in whether or not a ML barrel with shoot specific projectiles well.
But simply..., if you launch a patched round ball of .490 size with the same powder load that you launch a patched round ball of .530 size..., the .490 will drop less over the same distance because it has a higher muzzle velocity. You can compensate for that by upping the powder load for the .530 ball to get the same MV as the .490.
Now most folks who hunt with patched round ball limit their max range to 100 yards which is often + or - 25 yards under hunting conditions. At that range the difference on impact between the two bullets vs. a deer is negligible. Now the energy of either bullet is sufficient to kill deer out to 200 yards..., but how consistent is the shot placement for a particular rifle at that distance is the question.
When it comes to Elk or Moose, you can take them with .530 round ball at that range with a proper powder load, and you should be able to take them with a .490 ball, OR..., you can add some "insurance" by using an alloy bullet or using a conical. You get a harder bullet with alloys, and you get a heavier bullet with a conical, and deliver more energy on impact, but you often need to increase the powder load to get more consistent, flatter trajectory.
When it comes to accuracy, some 1:48 twist barrels will shoot .530 PRB very well..., I have one that does quite well. I have a 1:56 that shoots PRB even better. The 1:48 also shoots some conicals well, but the 1:56 only likes patched round ball. My hunting buddy has a 1:24 in .54 that also shoots PRB very well. All of the barrels that I mention in this paragraph were shot using 70 grains of 3Fg black powder.
I was taught that a 1:66 or + twist barrel will not shoot conicals well..., but the 3-Band Enfield repro from Pedersoli is a 1:78 twist and is used for target shooting with conicals. So again it's very tough to actually answer your question.
Conclusion
A 1:48 twist .50 caliber rifle should be accurate enough to allow you to compete on the local level with patched round ball with a good chance of winning, and will take deer out to 125 yards no problem. If you find a conical that will work, and you should be able to do so..., you should be able to take anything up to and including a moose again out to 100 yards. The same is true for stuff in .54.
As far as going beyond 125 yards..., conical or round ball, ..., that will depend on the quality of the individual barrel, and your ability to practice practice practice.
LD