Full disclosure: I am primarily shooting a smokeless ML, but I don't hotrod it. I usually load for similar velocities to standard ML loads, and not the 150gr equivalents, either. Now onto the rest…
I want shock AND exit wound. For all of the merits of the killing affect of shock, you will eventually need an exit wound and blood trail some day. And neither will cover for a bad shot as has been alluded to by other posters.
In my muzzle loader I use 325gr .458 or 250gr .452 FTX bullets and Harvester or MMP sabots. The 325s have never NOT given me an exit wound from any angle, and the blood trail is very impressive. I've only just begun to use the 250s (led to this because of recoil and availability of the 325, but I'm also a notorious tinkerer), but have had a good start so far (1/1) with exit wound and short tracking job. I'll be honest, a 250gr bullet in a 50 cal ML is on the light side, and I expect one to stay in there eventually if I'm not selective with my angles, but the one that I shot this season was from a VERY high angle and quartering away and exited the offside shoulder just fine. If that shot entry/exit was reversed then I'm sure that I would have been wishing that I had used the 325. I will likely end up using the 325s next season and just deal with the recoil.
I've had good success with the SST/Shockwave (same bullet, different sticker on the package), but only with the 300gr. Early in my hunting career I jumped straight from 200 to 300 when the 200s would not EVER give me an exit wound, and left sparse blood trails when the deer was not DRT. The 300gr SST/Shockwave answered this call, but can be difficult to find at a reasonable price… enter the 325 FTX. Once again, I want shock AND exit wound.
I took a young hunter/shooter out last Friday, and he used my CVA Optima V2 using a reduced load of BH209, a 300gr XTP mag, and an MMP short black sabot. Even in reduced loads I'd rather go lighter on powder than on bullet in an ML, with few exceptions.