Switch the spreads on the .44 and .50, drop the weight on the .44 by .5 and the STR req. should be increased by 1 for the .50. As far as names are concerned, have you considered Mountain Hawk? Granted, I don't know why anyone would want a DEagle when they could have a rifle that fires http://en.wikipedia.org/wiki/.950_JDJ... but to each their own.
The .50 DE is a touch lighter than the .44 DE and that's mainly because the .50 has less metal in the barrel assembly. Keeping them even would play to realism...
As well the .50 AE is more functional and more accurate than the .44 and .357 through the Desert Eagle. Why? I don't know, but all the research I've done over the past couple years for the gun indicates that the .50 AE fired out of the DE is generally more accurate than the .44 Magnum.
As far as rifles go I'm pretty satisfied with the selection already in game, "This Machine", "gobi campaign", and the "Anti-material rifle" all satisfy me pretty well. Though with the latest patch it seems I can't hit jack with "This Machine".
The STR requirement for the .50 DE should remain at 6, even though the 12.7MM is 7. I base this off of the Hunting Revolver and Ranger Sequoia, which both fire .45-75 ammo which is a rifle round, and they weigh .5 less than the Desert Eagle. By that the DE should be 6 strength.