The .44 mag is certainly a potent caliber, but compared to the .500 mag there's a big difference ballisticly. Muzzle energy for the .44 mag is around 900 ft-lb, while the 500 mag is 2300 ft-lb. Velocity is 1300 vs 1700 ft-sec. Of course either round can be loader "hotter" to increase these numbers, and a lot of variables need to be taken in to account too. But loading a .44 mag to equal the .500 mag ballisticly could be hazardous.
Both rounds are very good at doing what they were designed to do. I bought my 500 S&W for bear protection in Alaska because I wanted the best tool available for the job.