Hey there,
Congrats on your new D eagle. I tried to buy a Mark VII nickel version myself off Gunbroker a couple months ago, but somebody used the "buy it now" feature a second before I did
I did alot of researching before purchasing my Mark VII .44. The most relevant information I found was that if your only interested in shooting .44 magnum get the Mark VII or maybe even the first version. I beleive the Mark XIX uses a bigger/heavier slide needed for the .50 AE so full power loads are needed with the smaller calibers. If I recall correctly, I think i've seen some people claim success with some or all of the lower powered loads. Let's hope you have a good one.
If your XIX turns out to be a pain in the heinieyou can always swap out the .44 barrel and mags for .50 cal which should run much better or if you don't care for the .50 just sell/trade your XIX for a earlier model. Most people complain about the cost of .50 ammo, but when I was searching for .50 cal prices I was coming across boxes of the good stuff for a bit over $20 which is pretty good in my book.
That's stinks your .357 didn't run too well. I too thought about getting a .357 DE, but only if it will run the 125gr. JHP loads. I think the best .357's were the Mark I's.
Enjoy the DE
EDIT - Oh yeah...get yourself one of the Hogue rubber grips. Either of them are great and well worth it.