I have a DE XIX (50). First thing I did was rip that hard black plastic grip off it and replace it with a Hogue grip. You'll be gripping tight, and it helps to have the softer, more comfortable grip. It's alot of fun to shoot.
I also special ordered the 44 mag barrel and magazine. The .50AE cartidge base is the same size as .44MAG, so you just swap the barrel and magazine and your good to go. If you get the .357 barrel, it's more expensive and not easy to swap at the range, as you have to change the 'bolt carrier' or whatever. What that boils down to is a spring that shoots 10 yards away and turns into the color of whatever dirt it lays upon.
Getting the .44 barrel allows more shooting at reduced cost. I haven't tried 44 special yet. I don't know if it is powerful enough to cycle the action (seriously).
If you get the older, used model Desert Eagle, you can't swap the barrel if I remember right. If you get one, best to get the Model 19 (XIX, whatever). I love mine.